<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:471be96f-a088-4915-b13a-04727b2418a8,g:fa5b4026-b7b5-44f1-9dce-212feeb4a6e9-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.h2o-america.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="hto-20251231.xsd#CONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_169c8310-dfca-461c-ba90-107d98d86783" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_80864c85-2972-45c6-b6a3-40c2ac91bcac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_169c8310-dfca-461c-ba90-107d98d86783" xlink:to="loc_us-gaap_StatementTable_80864c85-2972-45c6-b6a3-40c2ac91bcac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_8569c1c5-5abb-4fc6-9407-5639c6241b91" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_80864c85-2972-45c6-b6a3-40c2ac91bcac" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_8569c1c5-5abb-4fc6-9407-5639c6241b91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_8569c1c5-5abb-4fc6-9407-5639c6241b91_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8569c1c5-5abb-4fc6-9407-5639c6241b91" xlink:to="loc_us-gaap_EquityComponentDomain_8569c1c5-5abb-4fc6-9407-5639c6241b91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_0b6dea6a-cff3-48f5-baa0-19e0498130d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8569c1c5-5abb-4fc6-9407-5639c6241b91" xlink:to="loc_us-gaap_EquityComponentDomain_0b6dea6a-cff3-48f5-baa0-19e0498130d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_f87e0e68-2394-434e-9d14-9d3938ba7d62" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0b6dea6a-cff3-48f5-baa0-19e0498130d3" xlink:to="loc_us-gaap_CommonStockMember_f87e0e68-2394-434e-9d14-9d3938ba7d62" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_39a8ec4d-35f8-42c9-b77a-e26b9c1fade4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0b6dea6a-cff3-48f5-baa0-19e0498130d3" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_39a8ec4d-35f8-42c9-b77a-e26b9c1fade4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_be867426-4e92-4ae6-91e5-ceabc925c4b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0b6dea6a-cff3-48f5-baa0-19e0498130d3" xlink:to="loc_us-gaap_RetainedEarningsMember_be867426-4e92-4ae6-91e5-ceabc925c4b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_905fa933-b819-4c0f-9022-287dcc41f921" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0b6dea6a-cff3-48f5-baa0-19e0498130d3" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_905fa933-b819-4c0f-9022-287dcc41f921" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_169c8310-dfca-461c-ba90-107d98d86783" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_d8f4e0fa-7f56-4034-a17b-088072c1ae72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_d8f4e0fa-7f56-4034-a17b-088072c1ae72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_b22d82b0-9f0a-41ca-9ea7-2af0d3df4b96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_StockholdersEquity_b22d82b0-9f0a-41ca-9ea7-2af0d3df4b96" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_4b70534f-45b6-4ca1-a364-38614230a551" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_NetIncomeLoss_4b70534f-45b6-4ca1-a364-38614230a551" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent_6aeeff6a-3187-482d-a3a8-576a0904bb02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent_6aeeff6a-3187-482d-a3a8-576a0904bb02" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent_b3606616-714f-4b6a-a3a5-faa457a41271" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent_b3606616-714f-4b6a-a3a5-faa457a41271" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_ee8041c6-a4d7-44a8-9c54-0df4c47e2afe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_ee8041c6-a4d7-44a8-9c54-0df4c47e2afe" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_21ece912-549a-49b5-b845-fdd10ca0f7e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_21ece912-549a-49b5-b845-fdd10ca0f7e5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_1d058195-2809-4e06-bd27-c05f697f42c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_1d058195-2809-4e06-bd27-c05f697f42c0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_efa599ad-ad8b-44ff-9f36-99c19873d974" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_efa599ad-ad8b-44ff-9f36-99c19873d974" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_941c42e7-bc7f-4361-8f87-8013d136821f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_941c42e7-bc7f-4361-8f87-8013d136821f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_949ef6a1-d526-4879-8137-7af528c0a2ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_949ef6a1-d526-4879-8137-7af528c0a2ce" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_359ff429-d2a4-4fd5-b3d7-9647f8081156" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_359ff429-d2a4-4fd5-b3d7-9647f8081156" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Dividends_a89fbd8f-97c0-4ddb-9e25-03098d31b545" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Dividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_bf8190a5-1470-4851-af12-55308df4dbab" xlink:to="loc_us-gaap_Dividends_a89fbd8f-97c0-4ddb-9e25-03098d31b545" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_33e9d497-fc48-4694-ab3c-249b429628d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_db644151-15b8-4a9d-8359-2f68dd44b142" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/OrganizationandOperationsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#OrganizationandOperationsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/OrganizationandOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_513625a2-921c-4cea-a210-50f227e07597" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_7dee7c00-74e9-42b4-be17-0c3c033e208b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_513625a2-921c-4cea-a210-50f227e07597" xlink:to="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_7dee7c00-74e9-42b4-be17-0c3c033e208b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_0aeb1ba7-e3b2-4380-9bd9-2e24f1338695" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_7dee7c00-74e9-42b4-be17-0c3c033e208b" xlink:to="loc_srt_ConsolidatedEntitiesAxis_0aeb1ba7-e3b2-4380-9bd9-2e24f1338695" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_0aeb1ba7-e3b2-4380-9bd9-2e24f1338695_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_0aeb1ba7-e3b2-4380-9bd9-2e24f1338695" xlink:to="loc_srt_ConsolidatedEntitiesDomain_0aeb1ba7-e3b2-4380-9bd9-2e24f1338695_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_3ff51429-dc3f-4c73-b3fb-eb5f8273a5cc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_0aeb1ba7-e3b2-4380-9bd9-2e24f1338695" xlink:to="loc_srt_ConsolidatedEntitiesDomain_3ff51429-dc3f-4c73-b3fb-eb5f8273a5cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SanJoseWaterCompanyMember_da9e23c4-2074-442a-a687-9877d90a7c32" xlink:href="hto-20251231.xsd#hto_SanJoseWaterCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_3ff51429-dc3f-4c73-b3fb-eb5f8273a5cc" xlink:to="loc_hto_SanJoseWaterCompanyMember_da9e23c4-2074-442a-a687-9877d90a7c32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_4fbd074a-3158-42f7-a7cb-8a1949c73265" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_3ff51429-dc3f-4c73-b3fb-eb5f8273a5cc" xlink:to="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_4fbd074a-3158-42f7-a7cb-8a1949c73265" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_VariableInterestEntitiesNumberOfEntities_8ec5725f-36a2-42fa-9d07-ef504998644c" xlink:href="hto-20251231.xsd#hto_VariableInterestEntitiesNumberOfEntities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_513625a2-921c-4cea-a210-50f227e07597" xlink:to="loc_hto_VariableInterestEntitiesNumberOfEntities_8ec5725f-36a2-42fa-9d07-ef504998644c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_VariableInterestEntityPrimaryBeneficiaryNumberOfSubsidiaries_2b0d1361-08e3-4df8-98d5-4c6575a2f1f5" xlink:href="hto-20251231.xsd#hto_VariableInterestEntityPrimaryBeneficiaryNumberOfSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_513625a2-921c-4cea-a210-50f227e07597" xlink:to="loc_hto_VariableInterestEntityPrimaryBeneficiaryNumberOfSubsidiaries_2b0d1361-08e3-4df8-98d5-4c6575a2f1f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityOwnershipPercentage_bd6daca5-6870-4cdf-8672-a79d3be5844d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_513625a2-921c-4cea-a210-50f227e07597" xlink:to="loc_us-gaap_VariableInterestEntityOwnershipPercentage_bd6daca5-6870-4cdf-8672-a79d3be5844d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesPropertyPlantandEquipmentandIntangibleAssetsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#SummaryofSignificantAccountingPoliciesPropertyPlantandEquipmentandIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesPropertyPlantandEquipmentandIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_7f55e58b-fd8c-4796-a3aa-f728e9593ae9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_17fab0a9-99b2-4aaa-bacc-86da8021b44a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PublicUtilityPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_7f55e58b-fd8c-4796-a3aa-f728e9593ae9" xlink:to="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_17fab0a9-99b2-4aaa-bacc-86da8021b44a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_d97cc46a-2606-441e-af86-e298dea1bffa" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_17fab0a9-99b2-4aaa-bacc-86da8021b44a" xlink:to="loc_srt_RangeAxis_d97cc46a-2606-441e-af86-e298dea1bffa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_d97cc46a-2606-441e-af86-e298dea1bffa_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_d97cc46a-2606-441e-af86-e298dea1bffa" xlink:to="loc_srt_RangeMember_d97cc46a-2606-441e-af86-e298dea1bffa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_53a9c9ec-586f-412a-bfc3-72623cf4835f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_d97cc46a-2606-441e-af86-e298dea1bffa" xlink:to="loc_srt_RangeMember_53a9c9ec-586f-412a-bfc3-72623cf4835f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_df1c53f9-5d0e-4b2c-8f4a-7a7b6632cf75" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_53a9c9ec-586f-412a-bfc3-72623cf4835f" xlink:to="loc_srt_MinimumMember_df1c53f9-5d0e-4b2c-8f4a-7a7b6632cf75" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_ee0c5258-6cfb-45d7-8395-cebf92c8550b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_53a9c9ec-586f-412a-bfc3-72623cf4835f" xlink:to="loc_srt_MaximumMember_ee0c5258-6cfb-45d7-8395-cebf92c8550b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityAxis_e2370278-4d62-4c83-80b8-e29d0c5d661d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PublicUtilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_17fab0a9-99b2-4aaa-bacc-86da8021b44a" xlink:to="loc_us-gaap_PublicUtilityAxis_e2370278-4d62-4c83-80b8-e29d0c5d661d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilityPlantDomain_e2370278-4d62-4c83-80b8-e29d0c5d661d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UtilityPlantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PublicUtilityAxis_e2370278-4d62-4c83-80b8-e29d0c5d661d" xlink:to="loc_us-gaap_UtilityPlantDomain_e2370278-4d62-4c83-80b8-e29d0c5d661d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilityPlantDomain_70065b31-870d-4a36-bb87-87ef66d99e6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UtilityPlantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PublicUtilityAxis_e2370278-4d62-4c83-80b8-e29d0c5d661d" xlink:to="loc_us-gaap_UtilityPlantDomain_70065b31-870d-4a36-bb87-87ef66d99e6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WaterPlantMember_126f4055-f4d3-40f2-943d-69de6aa0ffc4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WaterPlantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UtilityPlantDomain_70065b31-870d-4a36-bb87-87ef66d99e6a" xlink:to="loc_us-gaap_WaterPlantMember_126f4055-f4d3-40f2-943d-69de6aa0ffc4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_a1f738a8-ff36-4e7a-aa3d-58e5ee547462" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_7f55e58b-fd8c-4796-a3aa-f728e9593ae9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_a1f738a8-ff36-4e7a-aa3d-58e5ee547462" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentSourceOfSupply_530d44b8-b84e-454f-a58b-aee0f5efd6ba" xlink:href="hto-20251231.xsd#hto_PublicUtilitiesPropertyPlantAndEquipmentSourceOfSupply"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_a1f738a8-ff36-4e7a-aa3d-58e5ee547462" xlink:to="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentSourceOfSupply_530d44b8-b84e-454f-a58b-aee0f5efd6ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentPumpingPlant_4fb4f5fc-6142-4fd2-b8c8-2a3dd09f0c7c" xlink:href="hto-20251231.xsd#hto_PublicUtilitiesPropertyPlantAndEquipmentPumpingPlant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_a1f738a8-ff36-4e7a-aa3d-58e5ee547462" xlink:to="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentPumpingPlant_4fb4f5fc-6142-4fd2-b8c8-2a3dd09f0c7c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentWaterTreatmentPlant_77490cfb-4f9b-435a-88bb-f7ce53500f15" xlink:href="hto-20251231.xsd#hto_PublicUtilitiesPropertyPlantAndEquipmentWaterTreatmentPlant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_a1f738a8-ff36-4e7a-aa3d-58e5ee547462" xlink:to="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentWaterTreatmentPlant_77490cfb-4f9b-435a-88bb-f7ce53500f15" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmissionAndDistribution_51535147-2dfe-4125-a7e7-0bae74f2a39d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmissionAndDistribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_a1f738a8-ff36-4e7a-aa3d-58e5ee547462" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmissionAndDistribution_51535147-2dfe-4125-a7e7-0bae74f2a39d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentGeneralPlant_85620c0d-b246-4851-8386-f22487b864c1" xlink:href="hto-20251231.xsd#hto_PublicUtilitiesPropertyPlantAndEquipmentGeneralPlant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_a1f738a8-ff36-4e7a-aa3d-58e5ee547462" xlink:to="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentGeneralPlant_85620c0d-b246-4851-8386-f22487b864c1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentDepreciablePlantAndEquipment_ba78b6b2-7ced-4136-8f32-619aaeb5007f" xlink:href="hto-20251231.xsd#hto_PublicUtilitiesPropertyPlantAndEquipmentDepreciablePlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_a1f738a8-ff36-4e7a-aa3d-58e5ee547462" xlink:to="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentDepreciablePlantAndEquipment_ba78b6b2-7ced-4136-8f32-619aaeb5007f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_EstimatedUsefulLivesOfPlantAndEquipmentAbstract_e3de2c2b-66c5-4b7d-8379-daad2089d9de" xlink:href="hto-20251231.xsd#hto_EstimatedUsefulLivesOfPlantAndEquipmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_7f55e58b-fd8c-4796-a3aa-f728e9593ae9" xlink:to="loc_hto_EstimatedUsefulLivesOfPlantAndEquipmentAbstract_e3de2c2b-66c5-4b7d-8379-daad2089d9de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentSourceOfSupplyUsefulLife_4a530b19-351c-4523-b843-85e2d6197ec9" xlink:href="hto-20251231.xsd#hto_PublicUtilitiesPropertyPlantAndEquipmentSourceOfSupplyUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_EstimatedUsefulLivesOfPlantAndEquipmentAbstract_e3de2c2b-66c5-4b7d-8379-daad2089d9de" xlink:to="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentSourceOfSupplyUsefulLife_4a530b19-351c-4523-b843-85e2d6197ec9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentPumpingPlantUsefulLife_f71f3df1-4fd7-421c-a481-22f1f72dfa3d" xlink:href="hto-20251231.xsd#hto_PublicUtilitiesPropertyPlantAndEquipmentPumpingPlantUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_EstimatedUsefulLivesOfPlantAndEquipmentAbstract_e3de2c2b-66c5-4b7d-8379-daad2089d9de" xlink:to="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentPumpingPlantUsefulLife_f71f3df1-4fd7-421c-a481-22f1f72dfa3d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentWaterTreatmentPlantUsefulLife_b4b9e85d-1863-41be-b3a2-41eb56eebfa0" xlink:href="hto-20251231.xsd#hto_PublicUtilitiesPropertyPlantAndEquipmentWaterTreatmentPlantUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_EstimatedUsefulLivesOfPlantAndEquipmentAbstract_e3de2c2b-66c5-4b7d-8379-daad2089d9de" xlink:to="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentWaterTreatmentPlantUsefulLife_b4b9e85d-1863-41be-b3a2-41eb56eebfa0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmissionAndDistributionUsefulLife_cc6d0346-469e-4f8b-8d00-9c67273e3683" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmissionAndDistributionUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_EstimatedUsefulLivesOfPlantAndEquipmentAbstract_e3de2c2b-66c5-4b7d-8379-daad2089d9de" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmissionAndDistributionUsefulLife_cc6d0346-469e-4f8b-8d00-9c67273e3683" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentGeneralPlantUsefulLife_c3f0b2b4-8ba6-42c3-8b65-aa17bba67244" xlink:href="hto-20251231.xsd#hto_PublicUtilitiesPropertyPlantAndEquipmentGeneralPlantUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_EstimatedUsefulLivesOfPlantAndEquipmentAbstract_e3de2c2b-66c5-4b7d-8379-daad2089d9de" xlink:to="loc_hto_PublicUtilitiesPropertyPlantAndEquipmentGeneralPlantUsefulLife_c3f0b2b4-8ba6-42c3-8b65-aa17bba67244" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService_46c5ff74-a15c-4be0-a607-f93806111de7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_7f55e58b-fd8c-4796-a3aa-f728e9593ae9" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService_46c5ff74-a15c-4be0-a607-f93806111de7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_04250ac3-123a-49db-82c9-fff4684ab4ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_7f55e58b-fd8c-4796-a3aa-f728e9593ae9" xlink:to="loc_us-gaap_Depreciation_04250ac3-123a-49db-82c9-fff4684ab4ce" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestCostsCapitalized_470f7fec-a35e-4f7b-8555-37afbfb65843" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestCostsCapitalized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_7f55e58b-fd8c-4796-a3aa-f728e9593ae9" xlink:to="loc_us-gaap_InterestCostsCapitalized_470f7fec-a35e-4f7b-8555-37afbfb65843" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_EquityFundsCapitalized_5507705f-24fa-40f7-ba45-034be9cb8902" xlink:href="hto-20251231.xsd#hto_EquityFundsCapitalized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_7f55e58b-fd8c-4796-a3aa-f728e9593ae9" xlink:to="loc_hto_EquityFundsCapitalized_5507705f-24fa-40f7-ba45-034be9cb8902" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_680d86a5-38ef-4e33-8f82-1aed75c03f3a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_7f55e58b-fd8c-4796-a3aa-f728e9593ae9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_680d86a5-38ef-4e33-8f82-1aed75c03f3a" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesNonutilityPropertiesandRealEstateInvestmentsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#SummaryofSignificantAccountingPoliciesNonutilityPropertiesandRealEstateInvestmentsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesNonutilityPropertiesandRealEstateInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsLineItems_255b5713-240f-4456-ae94-9aca9a4d19ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsTable_9e4a0d98-cbfd-417b-bc37-452610c7a389" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_255b5713-240f-4456-ae94-9aca9a4d19ec" xlink:to="loc_us-gaap_ScheduleOfInvestmentsTable_9e4a0d98-cbfd-417b-bc37-452610c7a389" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b623090a-9622-454c-b2b3-a6023640985e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_9e4a0d98-cbfd-417b-bc37-452610c7a389" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b623090a-9622-454c-b2b3-a6023640985e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b623090a-9622-454c-b2b3-a6023640985e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b623090a-9622-454c-b2b3-a6023640985e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b623090a-9622-454c-b2b3-a6023640985e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1aa5fc7a-6677-4e5d-b42c-a95d489f87f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b623090a-9622-454c-b2b3-a6023640985e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1aa5fc7a-6677-4e5d-b42c-a95d489f87f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_087d36ed-e363-4fd9-9caf-c4b4dd878f95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BuildingAndBuildingImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1aa5fc7a-6677-4e5d-b42c-a95d489f87f8" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_087d36ed-e363-4fd9-9caf-c4b4dd878f95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_fd0007b3-598f-4550-b46b-6b698f538055" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_9e4a0d98-cbfd-417b-bc37-452610c7a389" xlink:to="loc_srt_RangeAxis_fd0007b3-598f-4550-b46b-6b698f538055" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_fd0007b3-598f-4550-b46b-6b698f538055_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_fd0007b3-598f-4550-b46b-6b698f538055" xlink:to="loc_srt_RangeMember_fd0007b3-598f-4550-b46b-6b698f538055_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_60e696f1-9c77-4311-8713-9e76fee1af1e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_fd0007b3-598f-4550-b46b-6b698f538055" xlink:to="loc_srt_RangeMember_60e696f1-9c77-4311-8713-9e76fee1af1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_4bc62630-56f2-4038-b496-ac22c461083e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_60e696f1-9c77-4311-8713-9e76fee1af1e" xlink:to="loc_srt_MinimumMember_4bc62630-56f2-4038-b496-ac22c461083e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_00632d09-334b-4b3f-94ef-860da6c98bf9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_60e696f1-9c77-4311-8713-9e76fee1af1e" xlink:to="loc_srt_MaximumMember_00632d09-334b-4b3f-94ef-860da6c98bf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateAbstract_e88c9e08-6b8f-4985-9afa-d8a65a865aa7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RealEstateAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_255b5713-240f-4456-ae94-9aca9a4d19ec" xlink:to="loc_us-gaap_RealEstateAbstract_e88c9e08-6b8f-4985-9afa-d8a65a865aa7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Land_e0fc9b76-4667-46a1-b57a-4006dedd8064" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Land"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_e88c9e08-6b8f-4985-9afa-d8a65a865aa7" xlink:to="loc_us-gaap_Land_e0fc9b76-4667-46a1-b57a-4006dedd8064" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_WholesaleWaterSupplyAssets_a3e550cd-aace-4a47-9bbe-6bbd6d7adb62" xlink:href="hto-20251231.xsd#hto_WholesaleWaterSupplyAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_e88c9e08-6b8f-4985-9afa-d8a65a865aa7" xlink:to="loc_hto_WholesaleWaterSupplyAssets_a3e550cd-aace-4a47-9bbe-6bbd6d7adb62" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentBuildingAndBuildingImprovements_97ecf7bb-f557-40d3-b432-bf8bd67f6ba4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentBuildingAndBuildingImprovements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_e88c9e08-6b8f-4985-9afa-d8a65a865aa7" xlink:to="loc_us-gaap_InvestmentBuildingAndBuildingImprovements_97ecf7bb-f557-40d3-b432-bf8bd67f6ba4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019c017a-e716-7a57-86b2-96ff7fc0aae4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_e88c9e08-6b8f-4985-9afa-d8a65a865aa7" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019c017a-e716-7a57-86b2-96ff7fc0aae4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019c017b-9a3b-7f7c-b71e-7ba01b79af0f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_e88c9e08-6b8f-4985-9afa-d8a65a865aa7" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019c017b-9a3b-7f7c-b71e-7ba01b79af0f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019c017b-08e2-7d8d-ba9c-f957e567ab50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateAbstract_e88c9e08-6b8f-4985-9afa-d8a65a865aa7" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019c017b-08e2-7d8d-ba9c-f957e567ab50" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateAndAccumulatedDepreciationLifeUsedForDepreciation1_00778f5d-5cbd-43c6-a36c-922755950671" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RealEstateAndAccumulatedDepreciationLifeUsedForDepreciation1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_255b5713-240f-4456-ae94-9aca9a4d19ec" xlink:to="loc_us-gaap_RealEstateAndAccumulatedDepreciationLifeUsedForDepreciation1_00778f5d-5cbd-43c6-a36c-922755950671" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesAccountsReceivableDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#SummaryofSignificantAccountingPoliciesAccountsReceivableDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesAccountsReceivableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_91019d8e-f4eb-4406-bcc6-db379a698236" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_a7ca14ff-79aa-4723-8b71-b751d027dc30" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_91019d8e-f4eb-4406-bcc6-db379a698236" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_a7ca14ff-79aa-4723-8b71-b751d027dc30" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_a54ecffe-7e12-4a76-aed9-a41062a11624" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_a7ca14ff-79aa-4723-8b71-b751d027dc30" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_a54ecffe-7e12-4a76-aed9-a41062a11624" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_a54ecffe-7e12-4a76-aed9-a41062a11624_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_a54ecffe-7e12-4a76-aed9-a41062a11624" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_a54ecffe-7e12-4a76-aed9-a41062a11624_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_5c639319-2166-42fc-9a1e-3e94c6bc2e20" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_a54ecffe-7e12-4a76-aed9-a41062a11624" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_5c639319-2166-42fc-9a1e-3e94c6bc2e20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RegulatoryAssetReductionMember_87d1469f-53a1-4cd9-a2f8-2fe584bc8609" xlink:href="hto-20251231.xsd#hto_RegulatoryAssetReductionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_5c639319-2166-42fc-9a1e-3e94c6bc2e20" xlink:to="loc_hto_RegulatoryAssetReductionMember_87d1469f-53a1-4cd9-a2f8-2fe584bc8609" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_a6e73265-f60d-4ea5-a54c-f3a5f80f029e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_5c639319-2166-42fc-9a1e-3e94c6bc2e20" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_a6e73265-f60d-4ea5-a54c-f3a5f80f029e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease_7affd576-5eeb-44fd-932f-0a8bff7b7200" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_91019d8e-f4eb-4406-bcc6-db379a698236" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease_7affd576-5eeb-44fd-932f-0a8bff7b7200" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesAdvancesforConstructionandContributionsinAidofConstructionDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#SummaryofSignificantAccountingPoliciesAdvancesforConstructionandContributionsinAidofConstructionDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesAdvancesforConstructionandContributionsinAidofConstructionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionLineItems_b9279c85-8bdb-4882-8fba-480a06fb244c" xlink:href="hto-20251231.xsd#hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionTable_32bb674c-c325-463c-845d-ae7597a93d26" xlink:href="hto-20251231.xsd#hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionLineItems_b9279c85-8bdb-4882-8fba-480a06fb244c" xlink:to="loc_hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionTable_32bb674c-c325-463c-845d-ae7597a93d26" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_a8d5df40-c98d-47aa-bc6b-d37752f5850f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionTable_32bb674c-c325-463c-845d-ae7597a93d26" xlink:to="loc_srt_StatementGeographicalAxis_a8d5df40-c98d-47aa-bc6b-d37752f5850f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_a8d5df40-c98d-47aa-bc6b-d37752f5850f_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_a8d5df40-c98d-47aa-bc6b-d37752f5850f" xlink:to="loc_srt_SegmentGeographicalDomain_a8d5df40-c98d-47aa-bc6b-d37752f5850f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_a1259200-b7ce-4108-a41a-88577c610535" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_a8d5df40-c98d-47aa-bc6b-d37752f5850f" xlink:to="loc_srt_SegmentGeographicalDomain_a1259200-b7ce-4108-a41a-88577c610535" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CA_0bbcdb3a-ea4b-4df1-a6f3-0355f481a004" xlink:href="https://xbrl.sec.gov/stpr/2025/stpr-2025.xsd#stpr_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_a1259200-b7ce-4108-a41a-88577c610535" xlink:to="loc_stpr_CA_0bbcdb3a-ea4b-4df1-a6f3-0355f481a004" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CT_7e5fd869-7e74-4330-91bc-3f1550e98d5a" xlink:href="https://xbrl.sec.gov/stpr/2025/stpr-2025.xsd#stpr_CT"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_a1259200-b7ce-4108-a41a-88577c610535" xlink:to="loc_stpr_CT_7e5fd869-7e74-4330-91bc-3f1550e98d5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_ME_65c00b54-034d-4737-9321-3b11657d82a1" xlink:href="https://xbrl.sec.gov/stpr/2025/stpr-2025.xsd#stpr_ME"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_a1259200-b7ce-4108-a41a-88577c610535" xlink:to="loc_stpr_ME_65c00b54-034d-4737-9321-3b11657d82a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ContractWithCustomerRefundLiabilityRefundPeriod_3df81ed7-34d0-41b9-92c2-33c32092ea5d" xlink:href="hto-20251231.xsd#hto_ContractWithCustomerRefundLiabilityRefundPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionLineItems_b9279c85-8bdb-4882-8fba-480a06fb244c" xlink:to="loc_hto_ContractWithCustomerRefundLiabilityRefundPeriod_3df81ed7-34d0-41b9-92c2-33c32092ea5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_7159ce19-3e72-430b-be61-1ddabc385819" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionLineItems_b9279c85-8bdb-4882-8fba-480a06fb244c" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_7159ce19-3e72-430b-be61-1ddabc385819" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CustomerAdvancesforConstructionNonRefundable_4eaa7073-d0da-4f46-a683-6b98e5a24c83" xlink:href="hto-20251231.xsd#hto_CustomerAdvancesforConstructionNonRefundable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionLineItems_b9279c85-8bdb-4882-8fba-480a06fb244c" xlink:to="loc_hto_CustomerAdvancesforConstructionNonRefundable_4eaa7073-d0da-4f46-a683-6b98e5a24c83" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CustomerAdvancesforConstructionRefundedonServiceConnections_f360f99e-4272-473f-9406-229ccacf7eef" xlink:href="hto-20251231.xsd#hto_CustomerAdvancesforConstructionRefundedonServiceConnections"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionLineItems_b9279c85-8bdb-4882-8fba-480a06fb244c" xlink:to="loc_hto_CustomerAdvancesforConstructionRefundedonServiceConnections_f360f99e-4272-473f-9406-229ccacf7eef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ContractWithCustomerRefundLiabilityFairValueDisclosure_c992d4ab-1d82-42e6-8a5f-31f8cf633651" xlink:href="hto-20251231.xsd#hto_ContractWithCustomerRefundLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_ScheduleOfEstimatedRefundsOfAdvancesForConstructionLineItems_b9279c85-8bdb-4882-8fba-480a06fb244c" xlink:to="loc_hto_ContractWithCustomerRefundLiabilityFairValueDisclosure_c992d4ab-1d82-42e6-8a5f-31f8cf633651" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesEarningsperShareDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#SummaryofSignificantAccountingPoliciesEarningsperShareDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesEarningsperShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_d40acdd0-bf38-465c-8f08-dd6ed350bb44" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_242f94ad-bc40-4dd5-843e-690762ae00d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_d40acdd0-bf38-465c-8f08-dd6ed350bb44" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_242f94ad-bc40-4dd5-843e-690762ae00d2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_9684743e-4e33-4b5f-864e-fab588360b90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_242f94ad-bc40-4dd5-843e-690762ae00d2" xlink:to="loc_us-gaap_StatementClassOfStockAxis_9684743e-4e33-4b5f-864e-fab588360b90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9684743e-4e33-4b5f-864e-fab588360b90_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9684743e-4e33-4b5f-864e-fab588360b90" xlink:to="loc_us-gaap_ClassOfStockDomain_9684743e-4e33-4b5f-864e-fab588360b90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_f502b12b-f475-40a0-b6a7-cb958ff4187d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9684743e-4e33-4b5f-864e-fab588360b90" xlink:to="loc_us-gaap_ClassOfStockDomain_f502b12b-f475-40a0-b6a7-cb958ff4187d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_516a93dc-2426-4b31-b258-e4e66aa18b8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_f502b12b-f475-40a0-b6a7-cb958ff4187d" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_516a93dc-2426-4b31-b258-e4e66aa18b8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_719925af-1532-4b20-9dad-1a4450f54170" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_d40acdd0-bf38-465c-8f08-dd6ed350bb44" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_719925af-1532-4b20-9dad-1a4450f54170" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesRelatedPartyTransactionDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#SummaryofSignificantAccountingPoliciesRelatedPartyTransactionDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/SummaryofSignificantAccountingPoliciesRelatedPartyTransactionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_1481fbb5-1c5b-4d0f-8552-2bea1d8fbe5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_1ceb092f-2f51-4442-a7a9-0478a3898e20" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_1481fbb5-1c5b-4d0f-8552-2bea1d8fbe5d" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_1ceb092f-2f51-4442-a7a9-0478a3898e20" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_ba06218f-dc98-4430-a4ae-d1dc6ca2c704" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_1ceb092f-2f51-4442-a7a9-0478a3898e20" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_ba06218f-dc98-4430-a4ae-d1dc6ca2c704" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_ba06218f-dc98-4430-a4ae-d1dc6ca2c704_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_ba06218f-dc98-4430-a4ae-d1dc6ca2c704" xlink:to="loc_us-gaap_RelatedPartyDomain_ba06218f-dc98-4430-a4ae-d1dc6ca2c704_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_e090904e-948a-4e3c-9447-95a82f0016a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_ba06218f-dc98-4430-a4ae-d1dc6ca2c704" xlink:to="loc_us-gaap_RelatedPartyDomain_e090904e-948a-4e3c-9447-95a82f0016a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_74c7514b-6563-4c5d-bc3f-6868ad6c573f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_e090904e-948a-4e3c-9447-95a82f0016a4" xlink:to="loc_us-gaap_RelatedPartyMember_74c7514b-6563-4c5d-bc3f-6868ad6c573f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_6237be66-5df4-4409-a6c0-2d95c9ea2b02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_1481fbb5-1c5b-4d0f-8552-2bea1d8fbe5d" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_6237be66-5df4-4409-a6c0-2d95c9ea2b02" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/RegulatoryMattersScheduleofRegulatoryAssetsNetDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#RegulatoryMattersScheduleofRegulatoryAssetsNetDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/RegulatoryMattersScheduleofRegulatoryAssetsNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetLineItems_e57197a9-26b0-432e-8cf2-f1958bfe390c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryAssetLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRegulatoryAssetsTable_903e659c-dc98-45d2-837f-8fd49afbb9e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRegulatoryAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RegulatoryAssetLineItems_e57197a9-26b0-432e-8cf2-f1958bfe390c" xlink:to="loc_us-gaap_ScheduleOfRegulatoryAssetsTable_903e659c-dc98-45d2-837f-8fd49afbb9e0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetAxis_5dc83c96-0316-4d79-a344-4a2f0cad2c86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryAssetAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRegulatoryAssetsTable_903e659c-dc98-45d2-837f-8fd49afbb9e0" xlink:to="loc_us-gaap_RegulatoryAssetAxis_5dc83c96-0316-4d79-a344-4a2f0cad2c86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetDomain_5dc83c96-0316-4d79-a344-4a2f0cad2c86_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RegulatoryAssetAxis_5dc83c96-0316-4d79-a344-4a2f0cad2c86" xlink:to="loc_us-gaap_RegulatoryAssetDomain_5dc83c96-0316-4d79-a344-4a2f0cad2c86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RegulatoryAssetAxis_5dc83c96-0316-4d79-a344-4a2f0cad2c86" xlink:to="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxChargesMember_5b2022c4-39f4-487b-865b-5952677fcb76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredIncomeTaxChargesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:to="loc_us-gaap_DeferredIncomeTaxChargesMember_5b2022c4-39f4-487b-865b-5952677fcb76" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_MontereyWaterRevenueAdjustmentMechanismMWRAMMember_9ad0b902-3e63-47b1-b8dd-caa73bdde8b1" xlink:href="hto-20251231.xsd#hto_MontereyWaterRevenueAdjustmentMechanismMWRAMMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:to="loc_hto_MontereyWaterRevenueAdjustmentMechanismMWRAMMember_9ad0b902-3e63-47b1-b8dd-caa73bdde8b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_BusinessCombinationsDebtPremiumMember_be8a964c-d010-42aa-b41d-7de7c35335d3" xlink:href="hto-20251231.xsd#hto_BusinessCombinationsDebtPremiumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:to="loc_hto_BusinessCombinationsDebtPremiumMember_be8a964c-d010-42aa-b41d-7de7c35335d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_EmployeeBenefitCostsMember_fae18498-69e0-4e98-944e-b75b95d6b12e" xlink:href="hto-20251231.xsd#hto_EmployeeBenefitCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:to="loc_hto_EmployeeBenefitCostsMember_fae18498-69e0-4e98-944e-b75b95d6b12e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CatastrophicEventMemorandumAccountsCEMAMember_de110c80-e0d0-46c1-9400-adab59542f1f" xlink:href="hto-20251231.xsd#hto_CatastrophicEventMemorandumAccountsCEMAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:to="loc_hto_CatastrophicEventMemorandumAccountsCEMAMember_de110c80-e0d0-46c1-9400-adab59542f1f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RevenueAdjustmentMechanismsMember_53c736a9-3dde-4331-8196-9012fe14dd1b" xlink:href="hto-20251231.xsd#hto_RevenueAdjustmentMechanismsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:to="loc_hto_RevenueAdjustmentMechanismsMember_53c736a9-3dde-4331-8196-9012fe14dd1b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CustomerAssistanceProgramBalancingAccountMember_dde2dc19-35c4-4ca2-a163-c37c3da4a7b8" xlink:href="hto-20251231.xsd#hto_CustomerAssistanceProgramBalancingAccountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:to="loc_hto_CustomerAssistanceProgramBalancingAccountMember_dde2dc19-35c4-4ca2-a163-c37c3da4a7b8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_WaterSupplyCostsMember_40417b8f-602e-48b5-82e8-4ec38deba8c2" xlink:href="hto-20251231.xsd#hto_WaterSupplyCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:to="loc_hto_WaterSupplyCostsMember_40417b8f-602e-48b5-82e8-4ec38deba8c2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementPlansCostsMember_4c0af5d7-15ff-4072-804e-7603dae8726c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionAndOtherPostretirementPlansCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:to="loc_us-gaap_PensionAndOtherPostretirementPlansCostsMember_4c0af5d7-15ff-4072-804e-7603dae8726c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_A2022GeneralRateCaseInterimMemorandumAccountMember_83f3584c-a154-49ee-a25b-8eebcf1c806b" xlink:href="hto-20251231.xsd#hto_A2022GeneralRateCaseInterimMemorandumAccountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:to="loc_hto_A2022GeneralRateCaseInterimMemorandumAccountMember_83f3584c-a154-49ee-a25b-8eebcf1c806b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_OtherRegulatoryAssetsMember_812431bc-02a7-439d-9e0f-fa72761d94be" xlink:href="hto-20251231.xsd#hto_OtherRegulatoryAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_72ee5c0d-17ef-4e5a-86e2-1deb8e570a84" xlink:to="loc_hto_OtherRegulatoryAssetsMember_812431bc-02a7-439d-9e0f-fa72761d94be" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityAxis_8b77504a-2cbc-46f7-aaae-aaf4ac808f11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryLiabilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRegulatoryAssetsTable_903e659c-dc98-45d2-837f-8fd49afbb9e0" xlink:to="loc_us-gaap_RegulatoryLiabilityAxis_8b77504a-2cbc-46f7-aaae-aaf4ac808f11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityDomain_8b77504a-2cbc-46f7-aaae-aaf4ac808f11_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryLiabilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RegulatoryLiabilityAxis_8b77504a-2cbc-46f7-aaae-aaf4ac808f11" xlink:to="loc_us-gaap_RegulatoryLiabilityDomain_8b77504a-2cbc-46f7-aaae-aaf4ac808f11_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityDomain_5b86bc51-0121-4506-a777-0cd81bf1b2eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryLiabilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RegulatoryLiabilityAxis_8b77504a-2cbc-46f7-aaae-aaf4ac808f11" xlink:to="loc_us-gaap_RegulatoryLiabilityDomain_5b86bc51-0121-4506-a777-0cd81bf1b2eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CostOfRemovalMember_f4348200-9b7f-4f83-8dda-f016ac881b6f" xlink:href="hto-20251231.xsd#hto_CostOfRemovalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryLiabilityDomain_5b86bc51-0121-4506-a777-0cd81bf1b2eb" xlink:to="loc_hto_CostOfRemovalMember_f4348200-9b7f-4f83-8dda-f016ac881b6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxChargesMember_3bd47318-a11f-4a57-b5a9-11ed208f0fb8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredIncomeTaxChargesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryLiabilityDomain_5b86bc51-0121-4506-a777-0cd81bf1b2eb" xlink:to="loc_us-gaap_DeferredIncomeTaxChargesMember_3bd47318-a11f-4a57-b5a9-11ed208f0fb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_UnrecognizedPensionsAndOtherPostretirementBenefitsMember_eab38198-5e4a-41c5-af33-6acb59ab000a" xlink:href="hto-20251231.xsd#hto_UnrecognizedPensionsAndOtherPostretirementBenefitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryLiabilityDomain_5b86bc51-0121-4506-a777-0cd81bf1b2eb" xlink:to="loc_hto_UnrecognizedPensionsAndOtherPostretirementBenefitsMember_eab38198-5e4a-41c5-af33-6acb59ab000a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PFASLegalSettlementProceedsMember_03d4fb19-2b01-410c-a01b-2d9c82b7635b" xlink:href="hto-20251231.xsd#hto_PFASLegalSettlementProceedsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryLiabilityDomain_5b86bc51-0121-4506-a777-0cd81bf1b2eb" xlink:to="loc_hto_PFASLegalSettlementProceedsMember_03d4fb19-2b01-410c-a01b-2d9c82b7635b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_EmployeeBenefitCostsMember_c624a438-f55a-4b30-a91c-6c9e35dc2474" xlink:href="hto-20251231.xsd#hto_EmployeeBenefitCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryLiabilityDomain_5b86bc51-0121-4506-a777-0cd81bf1b2eb" xlink:to="loc_hto_EmployeeBenefitCostsMember_c624a438-f55a-4b30-a91c-6c9e35dc2474" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RevenueAdjustmentMechanismsMember_0708f5eb-792f-40b7-bd3d-6ef35fd56cf8" xlink:href="hto-20251231.xsd#hto_RevenueAdjustmentMechanismsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryLiabilityDomain_5b86bc51-0121-4506-a777-0cd81bf1b2eb" xlink:to="loc_hto_RevenueAdjustmentMechanismsMember_0708f5eb-792f-40b7-bd3d-6ef35fd56cf8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_WaterSupplyCostsMember_6ee0b7e7-6de0-4366-bec4-77602ef4b417" xlink:href="hto-20251231.xsd#hto_WaterSupplyCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryLiabilityDomain_5b86bc51-0121-4506-a777-0cd81bf1b2eb" xlink:to="loc_hto_WaterSupplyCostsMember_6ee0b7e7-6de0-4366-bec4-77602ef4b417" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_OtherRegulatoryLiabilitiesMember_fa8188f9-d45f-42e9-990e-8fb83c40f608" xlink:href="hto-20251231.xsd#hto_OtherRegulatoryLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryLiabilityDomain_5b86bc51-0121-4506-a777-0cd81bf1b2eb" xlink:to="loc_hto_OtherRegulatoryLiabilitiesMember_fa8188f9-d45f-42e9-990e-8fb83c40f608" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_6393d433-70bd-4039-a4ee-06175516b85b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRegulatoryAssetsTable_903e659c-dc98-45d2-837f-8fd49afbb9e0" xlink:to="loc_srt_RangeAxis_6393d433-70bd-4039-a4ee-06175516b85b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_6393d433-70bd-4039-a4ee-06175516b85b_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_6393d433-70bd-4039-a4ee-06175516b85b" xlink:to="loc_srt_RangeMember_6393d433-70bd-4039-a4ee-06175516b85b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8dd146a4-af20-4deb-8d7c-adead275093a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_6393d433-70bd-4039-a4ee-06175516b85b" xlink:to="loc_srt_RangeMember_8dd146a4-af20-4deb-8d7c-adead275093a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_c9ffbe07-6c78-47d8-b5ad-656713fb22bc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8dd146a4-af20-4deb-8d7c-adead275093a" xlink:to="loc_srt_MinimumMember_c9ffbe07-6c78-47d8-b5ad-656713fb22bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_31788efe-553c-432b-948e-1c9447abe4d5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8dd146a4-af20-4deb-8d7c-adead275093a" xlink:to="loc_srt_MaximumMember_31788efe-553c-432b-948e-1c9447abe4d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetRegulatoryAssetsAbstract_472c79ab-92e2-4ed3-9233-697dbde8a770" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetRegulatoryAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetLineItems_e57197a9-26b0-432e-8cf2-f1958bfe390c" xlink:to="loc_us-gaap_NetRegulatoryAssetsAbstract_472c79ab-92e2-4ed3-9233-697dbde8a770" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssets_e495eb4b-2e85-451d-866b-1d90b3d2d832" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetRegulatoryAssetsAbstract_472c79ab-92e2-4ed3-9233-697dbde8a770" xlink:to="loc_us-gaap_RegulatoryAssets_e495eb4b-2e85-451d-866b-1d90b3d2d832" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsCurrent_c6f741a1-6f7e-40fc-a8d3-81e03ad727f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetRegulatoryAssetsAbstract_472c79ab-92e2-4ed3-9233-697dbde8a770" xlink:to="loc_us-gaap_RegulatoryAssetsCurrent_c6f741a1-6f7e-40fc-a8d3-81e03ad727f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_d7945dd9-6612-4101-8804-7b38387a0b43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetRegulatoryAssetsAbstract_472c79ab-92e2-4ed3-9233-697dbde8a770" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_d7945dd9-6612-4101-8804-7b38387a0b43" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_NetRegulatoryLiabilitiesAbstract_5b73ec75-9fd6-420a-9267-d5cec41268df" xlink:href="hto-20251231.xsd#hto_NetRegulatoryLiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetLineItems_e57197a9-26b0-432e-8cf2-f1958bfe390c" xlink:to="loc_hto_NetRegulatoryLiabilitiesAbstract_5b73ec75-9fd6-420a-9267-d5cec41268df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilities_15acd393-77fe-48a7-9d12-b21408b50322" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_NetRegulatoryLiabilitiesAbstract_5b73ec75-9fd6-420a-9267-d5cec41268df" xlink:to="loc_us-gaap_RegulatoryLiabilities_15acd393-77fe-48a7-9d12-b21408b50322" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityCurrent_8622dcdf-0bc8-47d2-bec9-200e58149638" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_NetRegulatoryLiabilitiesAbstract_5b73ec75-9fd6-420a-9267-d5cec41268df" xlink:to="loc_us-gaap_RegulatoryLiabilityCurrent_8622dcdf-0bc8-47d2-bec9-200e58149638" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityNoncurrent_c1005f3c-7ca6-45f2-824e-a87ee3e276fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_NetRegulatoryLiabilitiesAbstract_5b73ec75-9fd6-420a-9267-d5cec41268df" xlink:to="loc_us-gaap_RegulatoryLiabilityNoncurrent_c1005f3c-7ca6-45f2-824e-a87ee3e276fe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentCommonUsefulLife_10406a20-c012-423d-818f-1235cf9df398" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentCommonUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetLineItems_e57197a9-26b0-432e-8cf2-f1958bfe390c" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentCommonUsefulLife_10406a20-c012-423d-818f-1235cf9df398" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/CapitalizationDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#CapitalizationDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/CapitalizationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_838a418d-0669-40ad-af26-eea08649f362" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_838a418d-0669-40ad-af26-eea08649f362" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_c2a42ddd-693c-4bf1-b85e-c40b3e8caae6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_838a418d-0669-40ad-af26-eea08649f362" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_c2a42ddd-693c-4bf1-b85e-c40b3e8caae6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c2a42ddd-693c-4bf1-b85e-c40b3e8caae6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_c2a42ddd-693c-4bf1-b85e-c40b3e8caae6" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c2a42ddd-693c-4bf1-b85e-c40b3e8caae6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_53f00780-37a3-4a2e-8a72-b2e1edc45060" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_c2a42ddd-693c-4bf1-b85e-c40b3e8caae6" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_53f00780-37a3-4a2e-8a72-b2e1edc45060" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_AtTheMarketOfferingMember_faa45022-1628-48d3-8c03-1d7cf60e28b0" xlink:href="hto-20251231.xsd#hto_AtTheMarketOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_53f00780-37a3-4a2e-8a72-b2e1edc45060" xlink:to="loc_hto_AtTheMarketOfferingMember_faa45022-1628-48d3-8c03-1d7cf60e28b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_cf46ab9e-1c0a-48e0-b7f2-17a02fed3bc7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_cf46ab9e-1c0a-48e0-b7f2-17a02fed3bc7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_846c22bc-9dc5-49f1-aafc-92f2ed52467f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_846c22bc-9dc5-49f1-aafc-92f2ed52467f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_55f4a057-6ce1-4ed4-ba1b-93fac5cfb2da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_us-gaap_CommonStockSharesIssued_55f4a057-6ce1-4ed4-ba1b-93fac5cfb2da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_b55fa056-ae3d-4b69-b264-a2524078634a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_b55fa056-ae3d-4b69-b264-a2524078634a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_f38e1481-0164-4fce-8800-c561174115e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_f38e1481-0164-4fce-8800-c561174115e4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_dd3b080f-eefe-4710-b114-5f3ef2be1213" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_dd3b080f-eefe-4710-b114-5f3ef2be1213" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_c8955a5d-6c02-4fda-bf1b-d2380db88de4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_us-gaap_PreferredStockSharesIssued_c8955a5d-6c02-4fda-bf1b-d2380db88de4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_9d355c07-fe50-4e56-aa02-5d959ed5e588" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_9d355c07-fe50-4e56-aa02-5d959ed5e588" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SaleOfStockAggregateGrossSalesPrice_2319450b-cad5-4770-9e92-74cbece4885e" xlink:href="hto-20251231.xsd#hto_SaleOfStockAggregateGrossSalesPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_hto_SaleOfStockAggregateGrossSalesPrice_2319450b-cad5-4770-9e92-74cbece4885e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_3a8ca0c6-744a-4b47-aace-f4a00cdaeae3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_3a8ca0c6-744a-4b47-aace-f4a00cdaeae3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SaleOfStockWeightedAveragePricePerShare_96c7ad6d-a3a3-4102-bbf9-c6a49ded2966" xlink:href="hto-20251231.xsd#hto_SaleOfStockWeightedAveragePricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_hto_SaleOfStockWeightedAveragePricePerShare_96c7ad6d-a3a3-4102-bbf9-c6a49ded2966" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_cb6498ab-495a-4477-bd23-31db5aa5f762" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_cb6498ab-495a-4477-bd23-31db5aa5f762" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SaleOfStockTotalEquityDistributionAgreementRemaining_2f8fe34d-612b-4ee7-8adc-39ca7d925eff" xlink:href="hto-20251231.xsd#hto_SaleOfStockTotalEquityDistributionAgreementRemaining"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_9b929b58-786f-4a50-a98e-d61b6cc7e6bc" xlink:to="loc_hto_SaleOfStockTotalEquityDistributionAgreementRemaining_2f8fe34d-612b-4ee7-8adc-39ca7d925eff" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/LinesofCreditScheduleofLinesofCreditDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#LinesofCreditScheduleofLinesofCreditDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/LinesofCreditScheduleofLinesofCreditDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_b1bce729-dabf-40a1-b6f0-553ae3b884d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_0c8f58f4-169e-42cb-a984-c105b1081c3a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_b1bce729-dabf-40a1-b6f0-553ae3b884d1" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_0c8f58f4-169e-42cb-a984-c105b1081c3a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_ff515aea-3608-40b3-8a28-369ff62ce6fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_0c8f58f4-169e-42cb-a984-c105b1081c3a" xlink:to="loc_us-gaap_CreditFacilityAxis_ff515aea-3608-40b3-8a28-369ff62ce6fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_ff515aea-3608-40b3-8a28-369ff62ce6fc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_ff515aea-3608-40b3-8a28-369ff62ce6fc" xlink:to="loc_us-gaap_CreditFacilityDomain_ff515aea-3608-40b3-8a28-369ff62ce6fc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_7128621e-6d1f-4efe-9566-956b78b3f0dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_ff515aea-3608-40b3-8a28-369ff62ce6fc" xlink:to="loc_us-gaap_CreditFacilityDomain_7128621e-6d1f-4efe-9566-956b78b3f0dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_bdd6a42c-7d9a-44e7-b090-8c5904e17e87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_7128621e-6d1f-4efe-9566-956b78b3f0dd" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_bdd6a42c-7d9a-44e7-b090-8c5904e17e87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_e698a14c-2622-4886-a029-48d0075d69bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_0c8f58f4-169e-42cb-a984-c105b1081c3a" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_e698a14c-2622-4886-a029-48d0075d69bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_e698a14c-2622-4886-a029-48d0075d69bc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e698a14c-2622-4886-a029-48d0075d69bc" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_e698a14c-2622-4886-a029-48d0075d69bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_c71dfe9a-1d5b-48f5-83c0-ee6520796652" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e698a14c-2622-4886-a029-48d0075d69bc" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_c71dfe9a-1d5b-48f5-83c0-ee6520796652" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_298f3afb-74d1-41ee-876f-99303ac3ee85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_c71dfe9a-1d5b-48f5-83c0-ee6520796652" xlink:to="loc_us-gaap_LineOfCreditMember_298f3afb-74d1-41ee-876f-99303ac3ee85" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_4d395812-0db0-4f45-ac39-9ac58ac35575" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_0c8f58f4-169e-42cb-a984-c105b1081c3a" xlink:to="loc_us-gaap_DebtInstrumentAxis_4d395812-0db0-4f45-ac39-9ac58ac35575" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_4d395812-0db0-4f45-ac39-9ac58ac35575_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_4d395812-0db0-4f45-ac39-9ac58ac35575" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_4d395812-0db0-4f45-ac39-9ac58ac35575_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_9676c9a2-1fbb-411d-b5fd-098b17bb411c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_4d395812-0db0-4f45-ac39-9ac58ac35575" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_9676c9a2-1fbb-411d-b5fd-098b17bb411c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SyndicatedCreditAgreementMember_0b198fbd-883a-419f-9064-d47ad5125a35" xlink:href="hto-20251231.xsd#hto_SyndicatedCreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_9676c9a2-1fbb-411d-b5fd-098b17bb411c" xlink:to="loc_hto_SyndicatedCreditAgreementMember_0b198fbd-883a-419f-9064-d47ad5125a35" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_H2OAmericaSyndicatedCreditAgreementMaturingSeptember2030Member_dc967a5b-b104-44b5-854b-31b07f331c02" xlink:href="hto-20251231.xsd#hto_H2OAmericaSyndicatedCreditAgreementMaturingSeptember2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_SyndicatedCreditAgreementMember_0b198fbd-883a-419f-9064-d47ad5125a35" xlink:to="loc_hto_H2OAmericaSyndicatedCreditAgreementMaturingSeptember2030Member_dc967a5b-b104-44b5-854b-31b07f331c02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SJWCSyndicatedCreditAgreementMaturingSeptember2030Member_fc312d2b-e2d5-467d-9a5c-d2f0612e7a90" xlink:href="hto-20251231.xsd#hto_SJWCSyndicatedCreditAgreementMaturingSeptember2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_SyndicatedCreditAgreementMember_0b198fbd-883a-419f-9064-d47ad5125a35" xlink:to="loc_hto_SJWCSyndicatedCreditAgreementMaturingSeptember2030Member_fc312d2b-e2d5-467d-9a5c-d2f0612e7a90" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CTWSSyndicatedCreditAgreementMaturingSeptember2030Member_019bdeee-0be3-706c-bc6a-c91648c113b0" xlink:href="hto-20251231.xsd#hto_CTWSSyndicatedCreditAgreementMaturingSeptember2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_SyndicatedCreditAgreementMember_0b198fbd-883a-419f-9064-d47ad5125a35" xlink:to="loc_hto_CTWSSyndicatedCreditAgreementMaturingSeptember2030Member_019bdeee-0be3-706c-bc6a-c91648c113b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CWCSyndicatedCreditAgreementMaturingSeptember2030Member_3a699df3-85ac-4b7b-bd24-9ee4212616ef" xlink:href="hto-20251231.xsd#hto_CWCSyndicatedCreditAgreementMaturingSeptember2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_SyndicatedCreditAgreementMember_0b198fbd-883a-419f-9064-d47ad5125a35" xlink:to="loc_hto_CWCSyndicatedCreditAgreementMaturingSeptember2030Member_3a699df3-85ac-4b7b-bd24-9ee4212616ef" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_MWCSyndicatedCreditAgreementMaturingSeptember2030Member_faf77244-3511-4de6-af79-7e71ce4540ab" xlink:href="hto-20251231.xsd#hto_MWCSyndicatedCreditAgreementMaturingSeptember2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_SyndicatedCreditAgreementMember_0b198fbd-883a-419f-9064-d47ad5125a35" xlink:to="loc_hto_MWCSyndicatedCreditAgreementMaturingSeptember2030Member_faf77244-3511-4de6-af79-7e71ce4540ab" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SJWTXSyndicatedCreditAgreementMaturingSeptember2030Member_86975e78-b53d-49c1-91b8-edfd6af6e0b8" xlink:href="hto-20251231.xsd#hto_SJWTXSyndicatedCreditAgreementMaturingSeptember2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_SyndicatedCreditAgreementMember_0b198fbd-883a-419f-9064-d47ad5125a35" xlink:to="loc_hto_SJWTXSyndicatedCreditAgreementMaturingSeptember2030Member_86975e78-b53d-49c1-91b8-edfd6af6e0b8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SJWCCreditAgreementMaturingJune2026Member_fdadedb2-36d4-46ca-b4b1-1f07872310cc" xlink:href="hto-20251231.xsd#hto_SJWCCreditAgreementMaturingJune2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_9676c9a2-1fbb-411d-b5fd-098b17bb411c" xlink:to="loc_hto_SJWCCreditAgreementMaturingJune2026Member_fdadedb2-36d4-46ca-b4b1-1f07872310cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CTWSCreditAgreementMaturingAugust2028Member_8001fc1a-00aa-4700-b81c-ea15ba9e5e01" xlink:href="hto-20251231.xsd#hto_CTWSCreditAgreementMaturingAugust2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_9676c9a2-1fbb-411d-b5fd-098b17bb411c" xlink:to="loc_hto_CTWSCreditAgreementMaturingAugust2028Member_8001fc1a-00aa-4700-b81c-ea15ba9e5e01" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CTWSCreditAgreementMaturingMay2025Member_019bdeef-5d5e-7313-aee3-4bce2f13f05b" xlink:href="hto-20251231.xsd#hto_CTWSCreditAgreementMaturingMay2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_9676c9a2-1fbb-411d-b5fd-098b17bb411c" xlink:to="loc_hto_CTWSCreditAgreementMaturingMay2025Member_019bdeef-5d5e-7313-aee3-4bce2f13f05b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_ab76103d-e062-4b00-a8e1-11a6632caa14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_b1bce729-dabf-40a1-b6f0-553ae3b884d1" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_ab76103d-e062-4b00-a8e1-11a6632caa14" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_dadc6b15-d8d0-447c-9aa3-ea82e89c0a55" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_b1bce729-dabf-40a1-b6f0-553ae3b884d1" xlink:to="loc_us-gaap_LineOfCredit_dadc6b15-d8d0-447c-9aa3-ea82e89c0a55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_5d4b7631-e68c-42c0-9318-00e2c9814da4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_b1bce729-dabf-40a1-b6f0-553ae3b884d1" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_5d4b7631-e68c-42c0-9318-00e2c9814da4" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/LinesofCreditNarrativeDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#LinesofCreditNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/LinesofCreditNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_019c2781-abe5-721d-a06e-e905ece8e2ed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_093195a6-3011-4608-b3d0-450ac5bc4367" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019c2781-abe5-721d-a06e-e905ece8e2ed" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_093195a6-3011-4608-b3d0-450ac5bc4367" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_edf3eca6-d699-44da-a341-dc91efcdb253" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_093195a6-3011-4608-b3d0-450ac5bc4367" xlink:to="loc_us-gaap_CreditFacilityAxis_edf3eca6-d699-44da-a341-dc91efcdb253" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_edf3eca6-d699-44da-a341-dc91efcdb253_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_edf3eca6-d699-44da-a341-dc91efcdb253" xlink:to="loc_us-gaap_CreditFacilityDomain_edf3eca6-d699-44da-a341-dc91efcdb253_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_cde43910-fd1f-4c86-b00f-8f6203fb6777" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_edf3eca6-d699-44da-a341-dc91efcdb253" xlink:to="loc_us-gaap_CreditFacilityDomain_cde43910-fd1f-4c86-b00f-8f6203fb6777" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_69dac098-82c0-4f5b-8961-75a7eed8162e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_cde43910-fd1f-4c86-b00f-8f6203fb6777" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_69dac098-82c0-4f5b-8961-75a7eed8162e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_07064ce4-2e39-4d46-8772-a89a7b521898" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_093195a6-3011-4608-b3d0-450ac5bc4367" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_07064ce4-2e39-4d46-8772-a89a7b521898" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_07064ce4-2e39-4d46-8772-a89a7b521898_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_07064ce4-2e39-4d46-8772-a89a7b521898" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_07064ce4-2e39-4d46-8772-a89a7b521898_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_107c7328-2289-41e4-ae1d-b372d7da0efd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_07064ce4-2e39-4d46-8772-a89a7b521898" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_107c7328-2289-41e4-ae1d-b372d7da0efd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_6c4ff4ea-9f57-4d3d-b2a9-a3e8cc7c00d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_107c7328-2289-41e4-ae1d-b372d7da0efd" xlink:to="loc_us-gaap_LineOfCreditMember_6c4ff4ea-9f57-4d3d-b2a9-a3e8cc7c00d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019c2781-ceb6-79ce-b0d8-4160451458e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_093195a6-3011-4608-b3d0-450ac5bc4367" xlink:to="loc_us-gaap_DebtInstrumentAxis_019c2781-ceb6-79ce-b0d8-4160451458e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019c2781-ceb6-79ce-b0d8-4160451458e3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019c2781-ceb6-79ce-b0d8-4160451458e3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019c2781-ceb6-79ce-b0d8-4160451458e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019c2781-ceb6-7a87-a794-12425685eedd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019c2781-ceb6-79ce-b0d8-4160451458e3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019c2781-ceb6-7a87-a794-12425685eedd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CreditAgreementMember_019c2781-ceb6-75e5-acac-6cec90d9eef8" xlink:href="hto-20251231.xsd#hto_CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019c2781-ceb6-7a87-a794-12425685eedd" xlink:to="loc_hto_CreditAgreementMember_019c2781-ceb6-75e5-acac-6cec90d9eef8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CTWSCreditAgreementMaturingMay2025Member_019c2782-232e-79b3-a0b1-eb39fb9cbe41" xlink:href="hto-20251231.xsd#hto_CTWSCreditAgreementMaturingMay2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019c2781-ceb6-7a87-a794-12425685eedd" xlink:to="loc_hto_CTWSCreditAgreementMaturingMay2025Member_019c2782-232e-79b3-a0b1-eb39fb9cbe41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CTWSCreditAgreementMaturingAugust2028Member_019c2782-232e-71ce-a6b2-0bc727969d0a" xlink:href="hto-20251231.xsd#hto_CTWSCreditAgreementMaturingAugust2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019c2781-ceb6-7a87-a794-12425685eedd" xlink:to="loc_hto_CTWSCreditAgreementMaturingAugust2028Member_019c2782-232e-71ce-a6b2-0bc727969d0a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SJWCCreditAgreementMaturingJune2026Member_019c2782-232e-7f7a-b71c-c310614e514b" xlink:href="hto-20251231.xsd#hto_SJWCCreditAgreementMaturingJune2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019c2781-ceb6-7a87-a794-12425685eedd" xlink:to="loc_hto_SJWCCreditAgreementMaturingJune2026Member_019c2782-232e-7f7a-b71c-c310614e514b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019c2781-abe5-7a1f-a1eb-d79138be322d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019c2781-abe5-721d-a06e-e905ece8e2ed" xlink:to="loc_us-gaap_LineOfCredit_019c2781-abe5-7a1f-a1eb-d79138be322d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtWeightedAverageInterestRate_019c2781-abe5-7529-b46a-7967cf41579e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermDebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019c2781-abe5-721d-a06e-e905ece8e2ed" xlink:to="loc_us-gaap_ShortTermDebtWeightedAverageInterestRate_019c2781-abe5-7529-b46a-7967cf41579e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019c2781-abe5-7d3a-8919-8b15ebee962d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019c2781-abe5-721d-a06e-e905ece8e2ed" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019c2781-abe5-7d3a-8919-8b15ebee962d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019c2781-ceb6-7ee6-a237-031ab93838dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019c2781-abe5-721d-a06e-e905ece8e2ed" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019c2781-ceb6-7ee6-a237-031ab93838dc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_019c2d3b-f520-7876-94a6-f8e4f054951f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019c2781-abe5-721d-a06e-e905ece8e2ed" xlink:to="loc_us-gaap_DebtInstrumentTerm_019c2d3b-f520-7876-94a6-f8e4f054951f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_DebtInstrumentCovenantCapitalizationRatio_019c2781-f9a2-7ffe-8481-6b00687c0ea1" xlink:href="hto-20251231.xsd#hto_DebtInstrumentCovenantCapitalizationRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019c2781-abe5-721d-a06e-e905ece8e2ed" xlink:to="loc_hto_DebtInstrumentCovenantCapitalizationRatio_019c2781-f9a2-7ffe-8481-6b00687c0ea1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_019c2782-232e-7c99-b41b-12f83e26a37d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019c2781-abe5-721d-a06e-e905ece8e2ed" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_019c2782-232e-7c99-b41b-12f83e26a37d" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/LongTermDebtScheduleofLongtermDebtInstrumentsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#LongTermDebtScheduleofLongtermDebtInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/LongTermDebtScheduleofLongtermDebtInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01f83db9-8202-441b-b1db-97748b9c37dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_01f5b578-b7c8-4a0a-acbf-98e51bb785e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01f83db9-8202-441b-b1db-97748b9c37dd" xlink:to="loc_us-gaap_DebtInstrumentTable_01f5b578-b7c8-4a0a-acbf-98e51bb785e5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_0dcd2022-4271-4b83-bb5d-4d8e6604acc5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01f5b578-b7c8-4a0a-acbf-98e51bb785e5" xlink:to="loc_srt_ConsolidatedEntitiesAxis_0dcd2022-4271-4b83-bb5d-4d8e6604acc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_0dcd2022-4271-4b83-bb5d-4d8e6604acc5_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_0dcd2022-4271-4b83-bb5d-4d8e6604acc5" xlink:to="loc_srt_ConsolidatedEntitiesDomain_0dcd2022-4271-4b83-bb5d-4d8e6604acc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_6e442a66-f84d-4a88-b720-b0e82dd7741d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_0dcd2022-4271-4b83-bb5d-4d8e6604acc5" xlink:to="loc_srt_ConsolidatedEntitiesDomain_6e442a66-f84d-4a88-b720-b0e82dd7741d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ParentCompanyMember_20203bb4-3725-4207-8681-650ce5b1fbe9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ParentCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_6e442a66-f84d-4a88-b720-b0e82dd7741d" xlink:to="loc_srt_ParentCompanyMember_20203bb4-3725-4207-8681-650ce5b1fbe9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SanJoseWaterCompanyMember_534d7a60-9521-4881-8037-7411586209f2" xlink:href="hto-20251231.xsd#hto_SanJoseWaterCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_6e442a66-f84d-4a88-b720-b0e82dd7741d" xlink:to="loc_hto_SanJoseWaterCompanyMember_534d7a60-9521-4881-8037-7411586209f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ConnecticutWaterServiceInc.Member_d89d7024-a9ba-4ef4-bb6c-1e5e464d00a8" xlink:href="hto-20251231.xsd#hto_ConnecticutWaterServiceInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_6e442a66-f84d-4a88-b720-b0e82dd7741d" xlink:to="loc_hto_ConnecticutWaterServiceInc.Member_d89d7024-a9ba-4ef4-bb6c-1e5e464d00a8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ConnecticutWaterCompanyMember_b65f91eb-16ff-4811-adc0-d5d179cd3a58" xlink:href="hto-20251231.xsd#hto_ConnecticutWaterCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_6e442a66-f84d-4a88-b720-b0e82dd7741d" xlink:to="loc_hto_ConnecticutWaterCompanyMember_b65f91eb-16ff-4811-adc0-d5d179cd3a58" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_TWCInc.Member_793c6cab-f4c3-41c3-9826-0012a4f978d1" xlink:href="hto-20251231.xsd#hto_TWCInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_6e442a66-f84d-4a88-b720-b0e82dd7741d" xlink:to="loc_hto_TWCInc.Member_793c6cab-f4c3-41c3-9826-0012a4f978d1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_MaineWaterCompanyMember_e6363ef0-f31a-4912-956b-acd4a0f41fd5" xlink:href="hto-20251231.xsd#hto_MaineWaterCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_6e442a66-f84d-4a88-b720-b0e82dd7741d" xlink:to="loc_hto_MaineWaterCompanyMember_e6363ef0-f31a-4912-956b-acd4a0f41fd5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_6a8dc783-0627-47f1-962c-d024d1e491f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01f5b578-b7c8-4a0a-acbf-98e51bb785e5" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_6a8dc783-0627-47f1-962c-d024d1e491f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_6a8dc783-0627-47f1-962c-d024d1e491f5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_6a8dc783-0627-47f1-962c-d024d1e491f5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_6a8dc783-0627-47f1-962c-d024d1e491f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_e0d5bc66-4ac7-4044-8ce5-cb42eef54820" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_6a8dc783-0627-47f1-962c-d024d1e491f5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_e0d5bc66-4ac7-4044-8ce5-cb42eef54820" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_12842964-64e8-427c-bba0-bf88d1ae285b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e0d5bc66-4ac7-4044-8ce5-cb42eef54820" xlink:to="loc_us-gaap_SeniorNotesMember_12842964-64e8-427c-bba0-bf88d1ae285b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityBondsMember_60a19c70-4329-4370-864a-2f9e631e6e0a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PublicUtilityBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e0d5bc66-4ac7-4044-8ce5-cb42eef54820" xlink:to="loc_us-gaap_PublicUtilityBondsMember_60a19c70-4329-4370-864a-2f9e631e6e0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableToBanksMember_c99a2907-f92f-4b46-94e2-87c847724d32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NotesPayableToBanksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e0d5bc66-4ac7-4044-8ce5-cb42eef54820" xlink:to="loc_us-gaap_NotesPayableToBanksMember_c99a2907-f92f-4b46-94e2-87c847724d32" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RevolvingFundLoanMember_dc8e887f-675d-47df-8a15-5e4e7c790c76" xlink:href="hto-20251231.xsd#hto_RevolvingFundLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e0d5bc66-4ac7-4044-8ce5-cb42eef54820" xlink:to="loc_hto_RevolvingFundLoanMember_dc8e887f-675d-47df-8a15-5e4e7c790c76" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SellerFinancingDebtMember_0122d93b-0450-4151-9ca3-00fc2eb2d1ea" xlink:href="hto-20251231.xsd#hto_SellerFinancingDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e0d5bc66-4ac7-4044-8ce5-cb42eef54820" xlink:to="loc_hto_SellerFinancingDebtMember_0122d93b-0450-4151-9ca3-00fc2eb2d1ea" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_e741af80-2923-455c-8a56-19880dc4b65e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01f5b578-b7c8-4a0a-acbf-98e51bb785e5" xlink:to="loc_us-gaap_DebtInstrumentAxis_e741af80-2923-455c-8a56-19880dc4b65e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_e741af80-2923-455c-8a56-19880dc4b65e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_e741af80-2923-455c-8a56-19880dc4b65e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_e741af80-2923-455c-8a56-19880dc4b65e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_4c4784f6-753e-44ad-8c9a-0a29bdca9b18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_e741af80-2923-455c-8a56-19880dc4b65e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_4c4784f6-753e-44ad-8c9a-0a29bdca9b18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CaliforniaPollutionControlFinancingAuthorityRevenueBondsTotalMember_ffb7692b-2d79-4c92-8d81-6e9d147481b8" xlink:href="hto-20251231.xsd#hto_CaliforniaPollutionControlFinancingAuthorityRevenueBondsTotalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_4c4784f6-753e-44ad-8c9a-0a29bdca9b18" xlink:to="loc_hto_CaliforniaPollutionControlFinancingAuthorityRevenueBondsTotalMember_ffb7692b-2d79-4c92-8d81-6e9d147481b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ConnecticutInnovationsRevenueBondsVariableRateMember_5fc479c7-2fbe-458f-bb3e-20f76f8582d7" xlink:href="hto-20251231.xsd#hto_ConnecticutInnovationsRevenueBondsVariableRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_4c4784f6-753e-44ad-8c9a-0a29bdca9b18" xlink:to="loc_hto_ConnecticutInnovationsRevenueBondsVariableRateMember_5fc479c7-2fbe-458f-bb3e-20f76f8582d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_StateRevolvingFundLoansMember_42808030-60ec-492b-a61e-fe2baa321420" xlink:href="hto-20251231.xsd#hto_StateRevolvingFundLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_4c4784f6-753e-44ad-8c9a-0a29bdca9b18" xlink:to="loc_hto_StateRevolvingFundLoansMember_42808030-60ec-492b-a61e-fe2baa321420" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_30e5a3d2-f992-4b9a-9923-876f2179e2dc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01f5b578-b7c8-4a0a-acbf-98e51bb785e5" xlink:to="loc_srt_RangeAxis_30e5a3d2-f992-4b9a-9923-876f2179e2dc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_30e5a3d2-f992-4b9a-9923-876f2179e2dc_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_30e5a3d2-f992-4b9a-9923-876f2179e2dc" xlink:to="loc_srt_RangeMember_30e5a3d2-f992-4b9a-9923-876f2179e2dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_68cf9a2d-3072-4069-8d3d-37a3d6414f82" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_30e5a3d2-f992-4b9a-9923-876f2179e2dc" xlink:to="loc_srt_RangeMember_68cf9a2d-3072-4069-8d3d-37a3d6414f82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_3fa9b13c-932b-465d-9685-4487ebf653da" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_68cf9a2d-3072-4069-8d3d-37a3d6414f82" xlink:to="loc_srt_MinimumMember_3fa9b13c-932b-465d-9685-4487ebf653da" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_1a71df98-e324-49fb-bb7e-59ff71bdb348" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_68cf9a2d-3072-4069-8d3d-37a3d6414f82" xlink:to="loc_srt_MaximumMember_1a71df98-e324-49fb-bb7e-59ff71bdb348" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_82475a48-1df0-43d7-ac07-3b4e75810333" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01f83db9-8202-441b-b1db-97748b9c37dd" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_82475a48-1df0-43d7-ac07-3b4e75810333" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_9429eb5b-9119-4aaf-93ad-9b57ddbfa001" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01f83db9-8202-441b-b1db-97748b9c37dd" xlink:to="loc_us-gaap_LongTermDebt_9429eb5b-9119-4aaf-93ad-9b57ddbfa001" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_13dc3d62-154d-47e5-8df4-8f78dbb2b225" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01f83db9-8202-441b-b1db-97748b9c37dd" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_13dc3d62-154d-47e5-8df4-8f78dbb2b225" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_4da5d577-e400-4d74-bf4d-c7cd266e8e9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01f83db9-8202-441b-b1db-97748b9c37dd" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_4da5d577-e400-4d74-bf4d-c7cd266e8e9f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_ef4aeb95-7c93-45fd-a42b-3f4985fbb6f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01f83db9-8202-441b-b1db-97748b9c37dd" xlink:to="loc_us-gaap_LongTermDebtCurrent_ef4aeb95-7c93-45fd-a42b-3f4985fbb6f3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_42348a32-6f74-4f9c-ab82-abe2e6210acd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01f83db9-8202-441b-b1db-97748b9c37dd" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_42348a32-6f74-4f9c-ab82-abe2e6210acd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_5dd1843c-6aac-42b9-b200-6a702ca81084" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01f83db9-8202-441b-b1db-97748b9c37dd" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_5dd1843c-6aac-42b9-b200-6a702ca81084" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/LongTermDebtNarrativeDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#LongTermDebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/LongTermDebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_da5f9073-7e63-4811-abbd-98fe186ad527" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_6e4502e6-e7a5-452c-967d-5f94842baca8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_da5f9073-7e63-4811-abbd-98fe186ad527" xlink:to="loc_us-gaap_DebtInstrumentTable_6e4502e6-e7a5-452c-967d-5f94842baca8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_cb96cbe5-54b5-4f65-8b43-0cedde641a90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6e4502e6-e7a5-452c-967d-5f94842baca8" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_cb96cbe5-54b5-4f65-8b43-0cedde641a90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_cb96cbe5-54b5-4f65-8b43-0cedde641a90_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_cb96cbe5-54b5-4f65-8b43-0cedde641a90" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_cb96cbe5-54b5-4f65-8b43-0cedde641a90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_85d999b3-79e4-4b60-aa9d-9432e5b61e65" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_cb96cbe5-54b5-4f65-8b43-0cedde641a90" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_85d999b3-79e4-4b60-aa9d-9432e5b61e65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_850485cc-bd7f-47e6-b0bf-d39614d1bdbb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_85d999b3-79e4-4b60-aa9d-9432e5b61e65" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_850485cc-bd7f-47e6-b0bf-d39614d1bdbb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_e8989a97-2f78-454d-8f6d-f82942601d57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_85d999b3-79e4-4b60-aa9d-9432e5b61e65" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_e8989a97-2f78-454d-8f6d-f82942601d57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_229d21b3-07d8-476e-b4f4-fdd6e185ab2b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6e4502e6-e7a5-452c-967d-5f94842baca8" xlink:to="loc_srt_ConsolidatedEntitiesAxis_229d21b3-07d8-476e-b4f4-fdd6e185ab2b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_229d21b3-07d8-476e-b4f4-fdd6e185ab2b_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_229d21b3-07d8-476e-b4f4-fdd6e185ab2b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_229d21b3-07d8-476e-b4f4-fdd6e185ab2b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_aa03797e-fa49-44bd-a827-c69f52db61b5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_229d21b3-07d8-476e-b4f4-fdd6e185ab2b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_aa03797e-fa49-44bd-a827-c69f52db61b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SanJoseWaterCompanyMember_e64c4a0d-3519-455a-a288-24ebfc926701" xlink:href="hto-20251231.xsd#hto_SanJoseWaterCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_aa03797e-fa49-44bd-a827-c69f52db61b5" xlink:to="loc_hto_SanJoseWaterCompanyMember_e64c4a0d-3519-455a-a288-24ebfc926701" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ConnecticutWaterCompanyMember_c6bd6b97-aee1-4751-999e-3d2df067fef2" xlink:href="hto-20251231.xsd#hto_ConnecticutWaterCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_aa03797e-fa49-44bd-a827-c69f52db61b5" xlink:to="loc_hto_ConnecticutWaterCompanyMember_c6bd6b97-aee1-4751-999e-3d2df067fef2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_TexasWaterResourcesMember_246e5351-53d3-4151-bbfa-56a882361d64" xlink:href="hto-20251231.xsd#hto_TexasWaterResourcesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_aa03797e-fa49-44bd-a827-c69f52db61b5" xlink:to="loc_hto_TexasWaterResourcesMember_246e5351-53d3-4151-bbfa-56a882361d64" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_TWCInc.Member_cb6d0740-2a85-41ea-abb3-1255ad255544" xlink:href="hto-20251231.xsd#hto_TWCInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_aa03797e-fa49-44bd-a827-c69f52db61b5" xlink:to="loc_hto_TWCInc.Member_cb6d0740-2a85-41ea-abb3-1255ad255544" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_MaineWaterCompanyMember_e8fa935c-6f4b-4103-b41b-fccfb0d61659" xlink:href="hto-20251231.xsd#hto_MaineWaterCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_aa03797e-fa49-44bd-a827-c69f52db61b5" xlink:to="loc_hto_MaineWaterCompanyMember_e8fa935c-6f4b-4103-b41b-fccfb0d61659" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_a0b91513-5ba2-4191-902d-50f81f8c1cad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6e4502e6-e7a5-452c-967d-5f94842baca8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_a0b91513-5ba2-4191-902d-50f81f8c1cad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_a0b91513-5ba2-4191-902d-50f81f8c1cad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a0b91513-5ba2-4191-902d-50f81f8c1cad" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_a0b91513-5ba2-4191-902d-50f81f8c1cad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_d2772abc-7b1b-4425-a690-17b9c2256d88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a0b91513-5ba2-4191-902d-50f81f8c1cad" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_d2772abc-7b1b-4425-a690-17b9c2256d88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_5529373f-6d32-460b-8909-5f4a15c673ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_d2772abc-7b1b-4425-a690-17b9c2256d88" xlink:to="loc_us-gaap_SeniorNotesMember_5529373f-6d32-460b-8909-5f4a15c673ad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableToBanksMember_2221cf99-db2c-439d-9373-ee240a378b83" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NotesPayableToBanksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_d2772abc-7b1b-4425-a690-17b9c2256d88" xlink:to="loc_us-gaap_NotesPayableToBanksMember_2221cf99-db2c-439d-9373-ee240a378b83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_StateRevolvingFundLoansMember_019c275e-8e9d-72e4-a15b-bb2d3f7c716c" xlink:href="hto-20251231.xsd#hto_StateRevolvingFundLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_d2772abc-7b1b-4425-a690-17b9c2256d88" xlink:to="loc_hto_StateRevolvingFundLoansMember_019c275e-8e9d-72e4-a15b-bb2d3f7c716c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_2f0bd2b1-7e74-4a40-834d-1d4c5c643e02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_d2772abc-7b1b-4425-a690-17b9c2256d88" xlink:to="loc_us-gaap_UnsecuredDebtMember_2f0bd2b1-7e74-4a40-834d-1d4c5c643e02" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_48c6a71a-9fb6-4a39-8b03-372850c8f097" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6e4502e6-e7a5-452c-967d-5f94842baca8" xlink:to="loc_us-gaap_DebtInstrumentAxis_48c6a71a-9fb6-4a39-8b03-372850c8f097" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_48c6a71a-9fb6-4a39-8b03-372850c8f097_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_48c6a71a-9fb6-4a39-8b03-372850c8f097" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_48c6a71a-9fb6-4a39-8b03-372850c8f097_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_46996133-8fd2-4f17-b663-7abb06cc4dec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_48c6a71a-9fb6-4a39-8b03-372850c8f097" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_46996133-8fd2-4f17-b663-7abb06cc4dec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_A5.63SeniorNoteSeriesQMember_450efb16-e084-4589-a3cd-9bd6009b4da0" xlink:href="hto-20251231.xsd#hto_A5.63SeniorNoteSeriesQMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_46996133-8fd2-4f17-b663-7abb06cc4dec" xlink:to="loc_hto_A5.63SeniorNoteSeriesQMember_450efb16-e084-4589-a3cd-9bd6009b4da0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_A5.83SeniorNoteSeriesRMember_fd505682-0ca2-46eb-8b10-279126fdaed7" xlink:href="hto-20251231.xsd#hto_A5.83SeniorNoteSeriesRMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_46996133-8fd2-4f17-b663-7abb06cc4dec" xlink:to="loc_hto_A5.83SeniorNoteSeriesRMember_fd505682-0ca2-46eb-8b10-279126fdaed7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_A5.78SeniorNoteSeries2024Member_ff6c29ae-a9b1-4754-9806-116bc0dc833d" xlink:href="hto-20251231.xsd#hto_A5.78SeniorNoteSeries2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_46996133-8fd2-4f17-b663-7abb06cc4dec" xlink:to="loc_hto_A5.78SeniorNoteSeries2024Member_ff6c29ae-a9b1-4754-9806-116bc0dc833d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_A6.08SeniorNoteSeries2025Member_019b33fc-c39e-7a48-81aa-74fbbb41a8fe" xlink:href="hto-20251231.xsd#hto_A6.08SeniorNoteSeries2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_46996133-8fd2-4f17-b663-7abb06cc4dec" xlink:to="loc_hto_A6.08SeniorNoteSeries2025Member_019b33fc-c39e-7a48-81aa-74fbbb41a8fe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_A6.473PromissoryNoteDueNovember202054Member_d754426d-be6b-416d-83b7-5a9728e792fc" xlink:href="hto-20251231.xsd#hto_A6.473PromissoryNoteDueNovember202054Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_46996133-8fd2-4f17-b663-7abb06cc4dec" xlink:to="loc_hto_A6.473PromissoryNoteDueNovember202054Member_d754426d-be6b-416d-83b7-5a9728e792fc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_A6.68PromissoryNoteDueSeptember12055Member_1a0b5d5b-6554-4175-8490-be180e5c666a" xlink:href="hto-20251231.xsd#hto_A6.68PromissoryNoteDueSeptember12055Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_46996133-8fd2-4f17-b663-7abb06cc4dec" xlink:to="loc_hto_A6.68PromissoryNoteDueSeptember12055Member_1a0b5d5b-6554-4175-8490-be180e5c666a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SeriesXBondMember_019bdf2c-871d-78ee-9ac8-589dea7c4c8d" xlink:href="hto-20251231.xsd#hto_SeriesXBondMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_46996133-8fd2-4f17-b663-7abb06cc4dec" xlink:to="loc_hto_SeriesXBondMember_019bdf2c-871d-78ee-9ac8-589dea7c4c8d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SeriesYBondMember_019bdf2c-871d-75d8-8032-d1ef74de30b3" xlink:href="hto-20251231.xsd#hto_SeriesYBondMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_46996133-8fd2-4f17-b663-7abb06cc4dec" xlink:to="loc_hto_SeriesYBondMember_019bdf2c-871d-75d8-8032-d1ef74de30b3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_A6.70PromissoryNoteDueJuly202055Member_c020a0e4-89f9-41be-a138-7996feea4a54" xlink:href="hto-20251231.xsd#hto_A6.70PromissoryNoteDueJuly202055Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_46996133-8fd2-4f17-b663-7abb06cc4dec" xlink:to="loc_hto_A6.70PromissoryNoteDueJuly202055Member_c020a0e4-89f9-41be-a138-7996feea4a54" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionAxis_7098da2e-9921-439c-93e2-f304d5e8d5da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6e4502e6-e7a5-452c-967d-5f94842baca8" xlink:to="loc_us-gaap_AssetAcquisitionAxis_7098da2e-9921-439c-93e2-f304d5e8d5da" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_7098da2e-9921-439c-93e2-f304d5e8d5da_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetAcquisitionAxis_7098da2e-9921-439c-93e2-f304d5e8d5da" xlink:to="loc_us-gaap_AssetAcquisitionDomain_7098da2e-9921-439c-93e2-f304d5e8d5da_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_00fcc23b-0d23-40f7-8c20-2c70bb9139e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetAcquisitionAxis_7098da2e-9921-439c-93e2-f304d5e8d5da" xlink:to="loc_us-gaap_AssetAcquisitionDomain_00fcc23b-0d23-40f7-8c20-2c70bb9139e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_KTWaterResourceLPMember_29a04f8b-b037-4ca0-84d5-dbb79bf8d5c3" xlink:href="hto-20251231.xsd#hto_KTWaterResourceLPMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_00fcc23b-0d23-40f7-8c20-2c70bb9139e4" xlink:to="loc_hto_KTWaterResourceLPMember_29a04f8b-b037-4ca0-84d5-dbb79bf8d5c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_ffb004d2-477b-4a72-8d43-3ac8291f09be" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_da5f9073-7e63-4811-abbd-98fe186ad527" xlink:to="loc_us-gaap_LongTermDebtFairValue_ffb004d2-477b-4a72-8d43-3ac8291f09be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_d9e8209a-bd64-480f-a45a-b1285d980bc7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_da5f9073-7e63-4811-abbd-98fe186ad527" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_d9e8209a-bd64-480f-a45a-b1285d980bc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_d28f9093-5d8e-4c76-92f5-0d60e3c7bdb1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_da5f9073-7e63-4811-abbd-98fe186ad527" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_d28f9093-5d8e-4c76-92f5-0d60e3c7bdb1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_AssetAcquisitionPostClosingProductionPayment_7e756723-3096-4131-94dd-262bf2c08911" xlink:href="hto-20251231.xsd#hto_AssetAcquisitionPostClosingProductionPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_da5f9073-7e63-4811-abbd-98fe186ad527" xlink:to="loc_hto_AssetAcquisitionPostClosingProductionPayment_7e756723-3096-4131-94dd-262bf2c08911" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_AssetAcquisitionPeriodOfPostClosingProductionPayment_019c33dc-35ef-7ab0-ba8b-d66cf183bee5" xlink:href="hto-20251231.xsd#hto_AssetAcquisitionPeriodOfPostClosingProductionPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_da5f9073-7e63-4811-abbd-98fe186ad527" xlink:to="loc_hto_AssetAcquisitionPeriodOfPostClosingProductionPayment_019c33dc-35ef-7ab0-ba8b-d66cf183bee5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_c27e18a5-9c57-46c8-8e50-30bd443d5daf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_da5f9073-7e63-4811-abbd-98fe186ad527" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_c27e18a5-9c57-46c8-8e50-30bd443d5daf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019bdf2c-871d-767e-a9b0-d16cd780cad8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_da5f9073-7e63-4811-abbd-98fe186ad527" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019bdf2c-871d-767e-a9b0-d16cd780cad8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentDecreaseForgiveness_019bdf2c-871d-7a0e-972c-3d53fcc0621b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentDecreaseForgiveness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_da5f9073-7e63-4811-abbd-98fe186ad527" xlink:to="loc_us-gaap_DebtInstrumentDecreaseForgiveness_019bdf2c-871d-7a0e-972c-3d53fcc0621b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019bdf39-79c8-7335-9d67-d55041b224d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_da5f9073-7e63-4811-abbd-98fe186ad527" xlink:to="loc_us-gaap_LongTermDebt_019bdf39-79c8-7335-9d67-d55041b224d9" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#IncomeTaxesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxContingencyLineItems_660e4ab8-82ce-4cb6-b5f9-b34f8f7a4229" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxContingencyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxContingencyTable_7b791fea-ff37-441e-ae7e-7ebaa5ab339f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxContingencyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_660e4ab8-82ce-4cb6-b5f9-b34f8f7a4229" xlink:to="loc_us-gaap_IncomeTaxContingencyTable_7b791fea-ff37-441e-ae7e-7ebaa5ab339f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_a0e3e825-2008-48b6-bbf6-a1e5bdb53516" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxContingencyTable_7b791fea-ff37-441e-ae7e-7ebaa5ab339f" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_a0e3e825-2008-48b6-bbf6-a1e5bdb53516" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_a0e3e825-2008-48b6-bbf6-a1e5bdb53516_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_a0e3e825-2008-48b6-bbf6-a1e5bdb53516" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_a0e3e825-2008-48b6-bbf6-a1e5bdb53516_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_a9f2befa-c3e0-4cff-969b-105f0d580a3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_a0e3e825-2008-48b6-bbf6-a1e5bdb53516" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_a9f2befa-c3e0-4cff-969b-105f0d580a3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_019c53f2-664c-7466-9dc2-ea0603e2b282" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_a9f2befa-c3e0-4cff-969b-105f0d580a3e" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_019c53f2-664c-7466-9dc2-ea0603e2b282" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwards_9a1f9fe6-b3d4-45fd-b4bd-d0724008ee0c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLossCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_660e4ab8-82ce-4cb6-b5f9-b34f8f7a4229" xlink:to="loc_us-gaap_OperatingLossCarryforwards_9a1f9fe6-b3d4-45fd-b4bd-d0724008ee0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAmount_62ed2ae0-6b4f-4df2-a163-b453e7ae9908" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxCreditCarryforwardAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_660e4ab8-82ce-4cb6-b5f9-b34f8f7a4229" xlink:to="loc_us-gaap_TaxCreditCarryforwardAmount_62ed2ae0-6b4f-4df2-a163-b453e7ae9908" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_DeferredTaxLiabilitiesPeriodIncreaseDecrease_9c7ed2aa-f3c9-450b-9142-7b54136520ff" xlink:href="hto-20251231.xsd#hto_DeferredTaxLiabilitiesPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_660e4ab8-82ce-4cb6-b5f9-b34f8f7a4229" xlink:to="loc_hto_DeferredTaxLiabilitiesPeriodIncreaseDecrease_9c7ed2aa-f3c9-450b-9142-7b54136520ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_UnrecognizedTaxBenefitsGross_ab158caf-a247-4b62-942b-590f93eabd83" xlink:href="hto-20251231.xsd#hto_UnrecognizedTaxBenefitsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_660e4ab8-82ce-4cb6-b5f9-b34f8f7a4229" xlink:to="loc_hto_UnrecognizedTaxBenefitsGross_ab158caf-a247-4b62-942b-590f93eabd83" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_5a33d64f-7284-413a-badb-74657e65da48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_660e4ab8-82ce-4cb6-b5f9-b34f8f7a4229" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_5a33d64f-7284-413a-badb-74657e65da48" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_UnrecognizedTaxBenefitsDecreaseResultingFromReEvaluationOfReserve_e2da12f7-d8ea-4ceb-8bad-faee4f9b84f7" xlink:href="hto-20251231.xsd#hto_UnrecognizedTaxBenefitsDecreaseResultingFromReEvaluationOfReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_660e4ab8-82ce-4cb6-b5f9-b34f8f7a4229" xlink:to="loc_hto_UnrecognizedTaxBenefitsDecreaseResultingFromReEvaluationOfReserve_e2da12f7-d8ea-4ceb-8bad-faee4f9b84f7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued_51849d16-72a4-44a3-a4d4-3f2c4a29c3ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_660e4ab8-82ce-4cb6-b5f9-b34f8f7a4229" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued_51849d16-72a4-44a3-a4d4-3f2c4a29c3ef" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_082be85a-465e-4059-808b-48b051427c3a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_660e4ab8-82ce-4cb6-b5f9-b34f8f7a4229" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_082be85a-465e-4059-808b-48b051427c3a" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/IncomeTaxesScheduleofIncomeTaxesPaidNetofRefundsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#IncomeTaxesScheduleofIncomeTaxesPaidNetofRefundsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/IncomeTaxesScheduleofIncomeTaxesPaidNetofRefundsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019c27a0-4845-7ae7-9e0d-d6d2b39318d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_019c27a0-4845-7139-8e6b-08d39f6a9795" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidByIndividualJurisdictionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019c27a0-4845-7ae7-9e0d-d6d2b39318d6" xlink:to="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_019c27a0-4845-7139-8e6b-08d39f6a9795" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019c27a0-4845-7b10-a82b-071a96f98d2c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_019c27a0-4845-7139-8e6b-08d39f6a9795" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019c27a0-4845-7b10-a82b-071a96f98d2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019c27a0-4845-7b10-a82b-071a96f98d2c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019c27a0-4845-7b10-a82b-071a96f98d2c" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019c27a0-4845-7b10-a82b-071a96f98d2c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019c27a0-4845-7ed0-ba47-cc8011694692" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019c27a0-4845-7b10-a82b-071a96f98d2c" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019c27a0-4845-7ed0-ba47-cc8011694692" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_019c2d66-7f5d-707b-9bf5-5551d2e4915c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019c27a0-4845-7ed0-ba47-cc8011694692" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_019c2d66-7f5d-707b-9bf5-5551d2e4915c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_StateAndLocalJurisdictionMaterialAmountMember_019c91a0-c078-76ad-9b80-bf77aadf889c" xlink:href="hto-20251231.xsd#hto_StateAndLocalJurisdictionMaterialAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StateAndLocalJurisdictionMember_019c2d66-7f5d-707b-9bf5-5551d2e4915c" xlink:to="loc_hto_StateAndLocalJurisdictionMaterialAmountMember_019c91a0-c078-76ad-9b80-bf77aadf889c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CA_019c27a3-d5c5-79be-80b2-d4a0cbc62516" xlink:href="https://xbrl.sec.gov/stpr/2025/stpr-2025.xsd#stpr_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_StateAndLocalJurisdictionMaterialAmountMember_019c91a0-c078-76ad-9b80-bf77aadf889c" xlink:to="loc_stpr_CA_019c27a3-d5c5-79be-80b2-d4a0cbc62516" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CT_019c27a3-d5c5-7d90-b5b9-6359c9a621ca" xlink:href="https://xbrl.sec.gov/stpr/2025/stpr-2025.xsd#stpr_CT"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_StateAndLocalJurisdictionMaterialAmountMember_019c91a0-c078-76ad-9b80-bf77aadf889c" xlink:to="loc_stpr_CT_019c27a3-d5c5-7d90-b5b9-6359c9a621ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_TN_019c27a3-d5c5-7290-885f-49f0a7b482a4" xlink:href="https://xbrl.sec.gov/stpr/2025/stpr-2025.xsd#stpr_TN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_StateAndLocalJurisdictionMaterialAmountMember_019c91a0-c078-76ad-9b80-bf77aadf889c" xlink:to="loc_stpr_TN_019c27a3-d5c5-7290-885f-49f0a7b482a4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidFederalAfterRefundReceived_019c27a0-4845-7d13-9e1e-e27cbf7be847" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidFederalAfterRefundReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019c27a0-4845-7ae7-9e0d-d6d2b39318d6" xlink:to="loc_us-gaap_IncomeTaxPaidFederalAfterRefundReceived_019c27a0-4845-7d13-9e1e-e27cbf7be847" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived_019c27a0-4845-7251-819b-b207150ed2a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019c27a0-4845-7ae7-9e0d-d6d2b39318d6" xlink:to="loc_us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived_019c27a0-4845-7251-819b-b207150ed2a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidForeignAfterRefundReceived_019c27a0-4845-73dc-9c40-a180c556723b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidForeignAfterRefundReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019c27a0-4845-7ae7-9e0d-d6d2b39318d6" xlink:to="loc_us-gaap_IncomeTaxPaidForeignAfterRefundReceived_019c27a0-4845-73dc-9c40-a180c556723b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_019c27a0-4845-7ae2-ab2f-48b836248b73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019c27a0-4845-7ae7-9e0d-d6d2b39318d6" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_019c27a0-4845-7ae2-ab2f-48b836248b73" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/IntangibleAssetsNarrativeDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#IntangibleAssetsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/IntangibleAssetsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0b22fea2-5d4d-4bf1-89c1-aebb0abe900b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_b4828a18-68ed-4eff-b7a2-b04b603aad84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0b22fea2-5d4d-4bf1-89c1-aebb0abe900b" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_b4828a18-68ed-4eff-b7a2-b04b603aad84" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_c3864c45-cb59-4f15-ba3d-a4f25dd9638f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_b4828a18-68ed-4eff-b7a2-b04b603aad84" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_c3864c45-cb59-4f15-ba3d-a4f25dd9638f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_c3864c45-cb59-4f15-ba3d-a4f25dd9638f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_c3864c45-cb59-4f15-ba3d-a4f25dd9638f" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_c3864c45-cb59-4f15-ba3d-a4f25dd9638f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_47a2afe3-9866-4c2e-82a8-5311ffeb4265" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_c3864c45-cb59-4f15-ba3d-a4f25dd9638f" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_47a2afe3-9866-4c2e-82a8-5311ffeb4265" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UseRightsMember_94037efb-faa0-4f4c-8552-aec93a6ef3da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UseRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_47a2afe3-9866-4c2e-82a8-5311ffeb4265" xlink:to="loc_us-gaap_UseRightsMember_94037efb-faa0-4f4c-8552-aec93a6ef3da" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_896de2db-d244-4f4a-9dde-c44567d818b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_b4828a18-68ed-4eff-b7a2-b04b603aad84" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_896de2db-d244-4f4a-9dde-c44567d818b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_896de2db-d244-4f4a-9dde-c44567d818b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_896de2db-d244-4f4a-9dde-c44567d818b0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_896de2db-d244-4f4a-9dde-c44567d818b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_b9085490-7bb4-432e-a165-16109077a159" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_896de2db-d244-4f4a-9dde-c44567d818b0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_b9085490-7bb4-432e-a165-16109077a159" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PurchasePremiumForCustomerRelationshipsMember_2f85c1d7-e431-4e05-aa9f-072546bafdec" xlink:href="hto-20251231.xsd#hto_PurchasePremiumForCustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_b9085490-7bb4-432e-a165-16109077a159" xlink:to="loc_hto_PurchasePremiumForCustomerRelationshipsMember_2f85c1d7-e431-4e05-aa9f-072546bafdec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_088696e4-b76e-413c-8adf-329efa0ddefe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_b9085490-7bb4-432e-a165-16109077a159" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_088696e4-b76e-413c-8adf-329efa0ddefe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceAgreementsMember_fc59d06b-e02a-4cec-80be-6ad6c6616f27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ServiceAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_088696e4-b76e-413c-8adf-329efa0ddefe" xlink:to="loc_us-gaap_ServiceAgreementsMember_fc59d06b-e02a-4cec-80be-6ad6c6616f27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_c1214c23-7847-4e3c-b6bb-6af8af288a82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_088696e4-b76e-413c-8adf-329efa0ddefe" xlink:to="loc_us-gaap_CustomerRelationshipsMember_c1214c23-7847-4e3c-b6bb-6af8af288a82" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualRightsMember_49c3a3b7-d2bb-4fcb-aa94-04a545a80808" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractualRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_088696e4-b76e-413c-8adf-329efa0ddefe" xlink:to="loc_us-gaap_ContractualRightsMember_49c3a3b7-d2bb-4fcb-aa94-04a545a80808" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_7dfe0d7b-1886-4b4b-bcc6-8dda63670cdc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0b22fea2-5d4d-4bf1-89c1-aebb0abe900b" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_7dfe0d7b-1886-4b4b-bcc6-8dda63670cdc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_0f0aa434-26fd-4996-9e94-9280992a57a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0b22fea2-5d4d-4bf1-89c1-aebb0abe900b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_0f0aa434-26fd-4996-9e94-9280992a57a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_eb29dc3e-e11c-499f-974b-5c46ea622d95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0b22fea2-5d4d-4bf1-89c1-aebb0abe900b" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_eb29dc3e-e11c-499f-974b-5c46ea622d95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_b308e9b4-aa64-40bc-a0f1-6e8d1d6b228e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0b22fea2-5d4d-4bf1-89c1-aebb0abe900b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_b308e9b4-aa64-40bc-a0f1-6e8d1d6b228e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_a0d341f7-8555-4069-bbdf-ae63cab7a67a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_b308e9b4-aa64-40bc-a0f1-6e8d1d6b228e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_a0d341f7-8555-4069-bbdf-ae63cab7a67a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_b6cba984-1a9b-4bc6-92e7-c5b0cafe2641" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_b308e9b4-aa64-40bc-a0f1-6e8d1d6b228e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_b6cba984-1a9b-4bc6-92e7-c5b0cafe2641" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_a9857a58-081e-41e1-a9d5-92d28dd671a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_b308e9b4-aa64-40bc-a0f1-6e8d1d6b228e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_a9857a58-081e-41e1-a9d5-92d28dd671a5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_523bb655-a824-4d69-9ff6-351355ee471e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_b308e9b4-aa64-40bc-a0f1-6e8d1d6b228e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_523bb655-a824-4d69-9ff6-351355ee471e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_019c33f7-14a9-740e-a69e-990cc99dc32c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_b308e9b4-aa64-40bc-a0f1-6e8d1d6b228e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_019c33f7-14a9-740e-a69e-990cc99dc32c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_019c33f7-2d39-7852-a7c1-f5a66bdd7202" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_b308e9b4-aa64-40bc-a0f1-6e8d1d6b228e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_019c33f7-2d39-7852-a7c1-f5a66bdd7202" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/IntangibleAssetsScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#IntangibleAssetsScheduleofFiniteLivedIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/IntangibleAssetsScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6d45453f-c4a1-42c8-965e-629ba714e8e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ab8d3bc0-b1a6-4b23-8179-793da50b8150" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6d45453f-c4a1-42c8-965e-629ba714e8e9" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ab8d3bc0-b1a6-4b23-8179-793da50b8150" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_76cf071b-82fd-43cc-ae1c-aff947b1a9d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ab8d3bc0-b1a6-4b23-8179-793da50b8150" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_76cf071b-82fd-43cc-ae1c-aff947b1a9d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_76cf071b-82fd-43cc-ae1c-aff947b1a9d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_76cf071b-82fd-43cc-ae1c-aff947b1a9d8" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_76cf071b-82fd-43cc-ae1c-aff947b1a9d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_4ce28388-dff9-4eca-bc19-de7cee45e9f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_76cf071b-82fd-43cc-ae1c-aff947b1a9d8" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_4ce28388-dff9-4eca-bc19-de7cee45e9f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UseRightsMember_f108b682-4e34-49f6-84de-1c886aa75f28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UseRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_4ce28388-dff9-4eca-bc19-de7cee45e9f6" xlink:to="loc_us-gaap_UseRightsMember_f108b682-4e34-49f6-84de-1c886aa75f28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_7c77b3da-70ed-4b73-926c-2fa4a1f42b8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ab8d3bc0-b1a6-4b23-8179-793da50b8150" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_7c77b3da-70ed-4b73-926c-2fa4a1f42b8e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_7c77b3da-70ed-4b73-926c-2fa4a1f42b8e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_7c77b3da-70ed-4b73-926c-2fa4a1f42b8e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_7c77b3da-70ed-4b73-926c-2fa4a1f42b8e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_b1633ae3-2b7e-420a-ad5c-9957be1743d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_7c77b3da-70ed-4b73-926c-2fa4a1f42b8e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_b1633ae3-2b7e-420a-ad5c-9957be1743d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PurchasePremiumForCustomerRelationshipsMember_f017c67a-1354-4521-ba5c-53fc449306c6" xlink:href="hto-20251231.xsd#hto_PurchasePremiumForCustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_b1633ae3-2b7e-420a-ad5c-9957be1743d1" xlink:to="loc_hto_PurchasePremiumForCustomerRelationshipsMember_f017c67a-1354-4521-ba5c-53fc449306c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_010fb25b-4cef-45c2-8711-cc39ff0310b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_b1633ae3-2b7e-420a-ad5c-9957be1743d1" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_010fb25b-4cef-45c2-8711-cc39ff0310b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_f8becf51-a297-4c48-b6af-94f24f94ed28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6d45453f-c4a1-42c8-965e-629ba714e8e9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_f8becf51-a297-4c48-b6af-94f24f94ed28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_e2c4000b-645d-43dd-826d-9b82775f7b22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_f8becf51-a297-4c48-b6af-94f24f94ed28" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_e2c4000b-645d-43dd-826d-9b82775f7b22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_c0f4f2b0-be09-4ec4-a625-77b78aa73387" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_f8becf51-a297-4c48-b6af-94f24f94ed28" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_c0f4f2b0-be09-4ec4-a625-77b78aa73387" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_d2878fae-e54d-4759-a481-1ab5b957c0f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_f8becf51-a297-4c48-b6af-94f24f94ed28" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_d2878fae-e54d-4759-a481-1ab5b957c0f2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_04ee6027-7fb0-4e1d-9651-c6f750baf336" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_f8becf51-a297-4c48-b6af-94f24f94ed28" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_04ee6027-7fb0-4e1d-9651-c6f750baf336" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_c5d7044a-0510-4956-8235-a7a4547b4468" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_f8becf51-a297-4c48-b6af-94f24f94ed28" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_c5d7044a-0510-4956-8235-a7a4547b4468" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/CommitmentsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#CommitmentsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/CommitmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermPurchaseCommitmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentTable_5b3ea143-5acf-4d66-a9e8-5851d7a8acbb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermPurchaseCommitmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentTable_5b3ea143-5acf-4d66-a9e8-5851d7a8acbb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_MajorSupplierAxis_72fe824f-9b82-4c19-b188-51d0a569ea52" xlink:href="hto-20251231.xsd#hto_MajorSupplierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_5b3ea143-5acf-4d66-a9e8-5851d7a8acbb" xlink:to="loc_hto_MajorSupplierAxis_72fe824f-9b82-4c19-b188-51d0a569ea52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_MajorSupplierDomain_72fe824f-9b82-4c19-b188-51d0a569ea52_default" xlink:href="hto-20251231.xsd#hto_MajorSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_hto_MajorSupplierAxis_72fe824f-9b82-4c19-b188-51d0a569ea52" xlink:to="loc_hto_MajorSupplierDomain_72fe824f-9b82-4c19-b188-51d0a569ea52_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_MajorSupplierDomain_1ce56df6-2e12-4a72-b561-bd0d96ea8d1d" xlink:href="hto-20251231.xsd#hto_MajorSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_hto_MajorSupplierAxis_72fe824f-9b82-4c19-b188-51d0a569ea52" xlink:to="loc_hto_MajorSupplierDomain_1ce56df6-2e12-4a72-b561-bd0d96ea8d1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SantaClaraValleyWaterDistrictMember_796ecfd5-f187-4d9f-948c-4d787a7cb781" xlink:href="hto-20251231.xsd#hto_SantaClaraValleyWaterDistrictMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_MajorSupplierDomain_1ce56df6-2e12-4a72-b561-bd0d96ea8d1d" xlink:to="loc_hto_SantaClaraValleyWaterDistrictMember_796ecfd5-f187-4d9f-948c-4d787a7cb781" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_GuadalupeBlancoRiverAuthorityMember_962bb8cb-7d8b-4c9f-86ce-0ad75d5c587f" xlink:href="hto-20251231.xsd#hto_GuadalupeBlancoRiverAuthorityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_MajorSupplierDomain_1ce56df6-2e12-4a72-b561-bd0d96ea8d1d" xlink:to="loc_hto_GuadalupeBlancoRiverAuthorityMember_962bb8cb-7d8b-4c9f-86ce-0ad75d5c587f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_LowerColoradoRiverAuthorityMember_180f6a06-0646-4cff-865a-8be65b34911f" xlink:href="hto-20251231.xsd#hto_LowerColoradoRiverAuthorityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_MajorSupplierDomain_1ce56df6-2e12-4a72-b561-bd0d96ea8d1d" xlink:to="loc_hto_LowerColoradoRiverAuthorityMember_180f6a06-0646-4cff-865a-8be65b34911f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_dc66d008-40ff-4d0d-9784-ffc0d25162b3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_5b3ea143-5acf-4d66-a9e8-5851d7a8acbb" xlink:to="loc_srt_CounterpartyNameAxis_dc66d008-40ff-4d0d-9784-ffc0d25162b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_dc66d008-40ff-4d0d-9784-ffc0d25162b3_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_dc66d008-40ff-4d0d-9784-ffc0d25162b3" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_dc66d008-40ff-4d0d-9784-ffc0d25162b3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4a6c56d8-cb91-4642-9c21-28560a2a23cd" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_dc66d008-40ff-4d0d-9784-ffc0d25162b3" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4a6c56d8-cb91-4642-9c21-28560a2a23cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SouthCentralConnecticutRegionalWaterAuthorityMember_5a9651bf-be17-4a4f-ad43-cccd3d6771ed" xlink:href="hto-20251231.xsd#hto_SouthCentralConnecticutRegionalWaterAuthorityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4a6c56d8-cb91-4642-9c21-28560a2a23cd" xlink:to="loc_hto_SouthCentralConnecticutRegionalWaterAuthorityMember_5a9651bf-be17-4a4f-ad43-cccd3d6771ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_TheMetropolitanDistrictMember_1c5a44b3-a7bd-45ac-b63c-e41e8b78f4dd" xlink:href="hto-20251231.xsd#hto_TheMetropolitanDistrictMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4a6c56d8-cb91-4642-9c21-28560a2a23cd" xlink:to="loc_hto_TheMetropolitanDistrictMember_1c5a44b3-a7bd-45ac-b63c-e41e8b78f4dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_KennebecWaterDistrictMember_940c8455-a1ff-407d-a2e1-4765195e5b30" xlink:href="hto-20251231.xsd#hto_KennebecWaterDistrictMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4a6c56d8-cb91-4642-9c21-28560a2a23cd" xlink:to="loc_hto_KennebecWaterDistrictMember_940c8455-a1ff-407d-a2e1-4765195e5b30" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_InternationalUnionOfOperatingEngineersMember_b82457ac-10ad-4253-87fc-80531363fc9d" xlink:href="hto-20251231.xsd#hto_InternationalUnionOfOperatingEngineersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4a6c56d8-cb91-4642-9c21-28560a2a23cd" xlink:to="loc_hto_InternationalUnionOfOperatingEngineersMember_b82457ac-10ad-4253-87fc-80531363fc9d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_9f9f0d40-0847-4dbf-b3e9-5e3e8d0d89bd" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_5b3ea143-5acf-4d66-a9e8-5851d7a8acbb" xlink:to="loc_srt_RangeAxis_9f9f0d40-0847-4dbf-b3e9-5e3e8d0d89bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_9f9f0d40-0847-4dbf-b3e9-5e3e8d0d89bd_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_9f9f0d40-0847-4dbf-b3e9-5e3e8d0d89bd" xlink:to="loc_srt_RangeMember_9f9f0d40-0847-4dbf-b3e9-5e3e8d0d89bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_a0a1c2a3-1ac7-4601-a93a-101d88cc7da7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_9f9f0d40-0847-4dbf-b3e9-5e3e8d0d89bd" xlink:to="loc_srt_RangeMember_a0a1c2a3-1ac7-4601-a93a-101d88cc7da7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_e12c17a7-e588-4f3b-8578-b3cf2c47db1b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_a0a1c2a3-1ac7-4601-a93a-101d88cc7da7" xlink:to="loc_srt_MaximumMember_e12c17a7-e588-4f3b-8578-b3cf2c47db1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_10791306-8068-4825-815f-277bcb16db39" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_5b3ea143-5acf-4d66-a9e8-5851d7a8acbb" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_10791306-8068-4825-815f-277bcb16db39" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_10791306-8068-4825-815f-277bcb16db39_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_10791306-8068-4825-815f-277bcb16db39" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_10791306-8068-4825-815f-277bcb16db39_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_7407c0d1-33a6-46ee-b46e-cf1ac7c768a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_10791306-8068-4825-815f-277bcb16db39" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_7407c0d1-33a6-46ee-b46e-cf1ac7c768a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CapacityAgreementMember_34f76315-18fd-46ef-b39e-3e2f8763a13d" xlink:href="hto-20251231.xsd#hto_CapacityAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_7407c0d1-33a6-46ee-b46e-cf1ac7c768a2" xlink:to="loc_hto_CapacityAgreementMember_34f76315-18fd-46ef-b39e-3e2f8763a13d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_98476bcf-28ac-44e3-9a9d-ae22e8d7e8e4" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_5b3ea143-5acf-4d66-a9e8-5851d7a8acbb" xlink:to="loc_dei_LegalEntityAxis_98476bcf-28ac-44e3-9a9d-ae22e8d7e8e4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_98476bcf-28ac-44e3-9a9d-ae22e8d7e8e4_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_98476bcf-28ac-44e3-9a9d-ae22e8d7e8e4" xlink:to="loc_dei_EntityDomain_98476bcf-28ac-44e3-9a9d-ae22e8d7e8e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_350cc2b4-afac-4b22-9e8b-47bae4b4e75c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_98476bcf-28ac-44e3-9a9d-ae22e8d7e8e4" xlink:to="loc_dei_EntityDomain_350cc2b4-afac-4b22-9e8b-47bae4b4e75c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SubsidiaryOneMember_bec37bdf-b820-4fd6-9b98-f5d57f2dd336" xlink:href="hto-20251231.xsd#hto_SubsidiaryOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_350cc2b4-afac-4b22-9e8b-47bae4b4e75c" xlink:to="loc_hto_SubsidiaryOneMember_bec37bdf-b820-4fd6-9b98-f5d57f2dd336" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_66b6b480-e280-4381-9412-cffdc5d6758d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_5b3ea143-5acf-4d66-a9e8-5851d7a8acbb" xlink:to="loc_srt_ConsolidatedEntitiesAxis_66b6b480-e280-4381-9412-cffdc5d6758d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_66b6b480-e280-4381-9412-cffdc5d6758d_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_66b6b480-e280-4381-9412-cffdc5d6758d" xlink:to="loc_srt_ConsolidatedEntitiesDomain_66b6b480-e280-4381-9412-cffdc5d6758d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_3aca538b-24b1-431e-b835-6bc23482cb88" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_66b6b480-e280-4381-9412-cffdc5d6758d" xlink:to="loc_srt_ConsolidatedEntitiesDomain_3aca538b-24b1-431e-b835-6bc23482cb88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ParentCompanyMember_9f1f7d57-a25a-490e-ad51-650bfd13a5ae" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ParentCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_3aca538b-24b1-431e-b835-6bc23482cb88" xlink:to="loc_srt_ParentCompanyMember_9f1f7d57-a25a-490e-ad51-650bfd13a5ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_33630ffb-1e32-49d3-8ce2-c0e0c513a39e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_5b3ea143-5acf-4d66-a9e8-5851d7a8acbb" xlink:to="loc_srt_TitleOfIndividualAxis_33630ffb-1e32-49d3-8ce2-c0e0c513a39e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_33630ffb-1e32-49d3-8ce2-c0e0c513a39e_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_33630ffb-1e32-49d3-8ce2-c0e0c513a39e" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_33630ffb-1e32-49d3-8ce2-c0e0c513a39e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_c4fd76cf-94c2-4d36-84ea-001dfb22c999" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_33630ffb-1e32-49d3-8ce2-c0e0c513a39e" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_c4fd76cf-94c2-4d36-84ea-001dfb22c999" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_UnionMemberMember_66116d15-ea75-476a-bd9f-75379737ed56" xlink:href="hto-20251231.xsd#hto_UnionMemberMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_c4fd76cf-94c2-4d36-84ea-001dfb22c999" xlink:to="loc_hto_UnionMemberMember_66116d15-ea75-476a-bd9f-75379737ed56" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_MasterContractNegotiatedTermForDeliverySchedules_2ad06628-e425-4d08-becd-f18adbc9c3c7" xlink:href="hto-20251231.xsd#hto_MasterContractNegotiatedTermForDeliverySchedules"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_MasterContractNegotiatedTermForDeliverySchedules_2ad06628-e425-4d08-becd-f18adbc9c3c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PurchasedWaterGallons_133e338e-855b-4e93-a174-ce7d7596d1e7" xlink:href="hto-20251231.xsd#hto_PurchasedWaterGallons"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_PurchasedWaterGallons_133e338e-855b-4e93-a174-ce7d7596d1e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfPurchasedWater_abab6aa7-30d8-44a6-ab7f-d515c359cc82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfPurchasedWater"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_us-gaap_CostOfPurchasedWater_abab6aa7-30d8-44a6-ab7f-d515c359cc82" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ReductioninDeliverySchedulePercent_d9c596fb-40eb-4edb-a27b-589a077c8381" xlink:href="hto-20251231.xsd#hto_ReductioninDeliverySchedulePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_ReductioninDeliverySchedulePercent_d9c596fb-40eb-4edb-a27b-589a077c8381" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_LongTermPurchaseCommitmentMinimumPercentageRequiredNextTwelveMonths_a51bb27b-df51-48f4-bf57-dc747956ebdd" xlink:href="hto-20251231.xsd#hto_LongTermPurchaseCommitmentMinimumPercentageRequiredNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_LongTermPurchaseCommitmentMinimumPercentageRequiredNextTwelveMonths_a51bb27b-df51-48f4-bf57-dc747956ebdd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_LongTermPurchaseCommitmentMinimumVolumeRequiredNextTwelveMonths_9b465cc5-e635-4476-ab98-a51514acf7ce" xlink:href="hto-20251231.xsd#hto_LongTermPurchaseCommitmentMinimumVolumeRequiredNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_LongTermPurchaseCommitmentMinimumVolumeRequiredNextTwelveMonths_9b465cc5-e635-4476-ab98-a51514acf7ce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInNextTwelveMonths_82c8464f-d19b-4b0d-93bd-de53f96c8959" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PurchaseObligationDueInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_us-gaap_PurchaseObligationDueInNextTwelveMonths_82c8464f-d19b-4b0d-93bd-de53f96c8959" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_LongTermPurchaseCommitmentFixedPrice_7ff3c9a5-d7a9-4557-aacc-b9ab086ac199" xlink:href="hto-20251231.xsd#hto_LongTermPurchaseCommitmentFixedPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_LongTermPurchaseCommitmentFixedPrice_7ff3c9a5-d7a9-4557-aacc-b9ab086ac199" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PublicUtilitiesServiceConnections_043d8b1a-ba2f-41ba-8ffb-db0bc8cced46" xlink:href="hto-20251231.xsd#hto_PublicUtilitiesServiceConnections"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_PublicUtilitiesServiceConnections_043d8b1a-ba2f-41ba-8ffb-db0bc8cced46" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ServiceAgreementTermOfContract_81fdead0-f356-4aed-b54c-bd419be04523" xlink:href="hto-20251231.xsd#hto_ServiceAgreementTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_ServiceAgreementTermOfContract_81fdead0-f356-4aed-b54c-bd419be04523" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ServiceAgreementRenewalTerm_698efd47-472d-4158-9029-95d65265333e" xlink:href="hto-20251231.xsd#hto_ServiceAgreementRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_ServiceAgreementRenewalTerm_698efd47-472d-4158-9029-95d65265333e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ServiceAgreementUpfrontConcessionFee_cab36caa-64dd-49a7-9541-cd4d76052df5" xlink:href="hto-20251231.xsd#hto_ServiceAgreementUpfrontConcessionFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_ServiceAgreementUpfrontConcessionFee_cab36caa-64dd-49a7-9541-cd4d76052df5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ServiceAgreementAnnualRentExpense_f87e5600-d2ca-4dae-986f-eb4a6c28db5e" xlink:href="hto-20251231.xsd#hto_ServiceAgreementAnnualRentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_ServiceAgreementAnnualRentExpense_f87e5600-d2ca-4dae-986f-eb4a6c28db5e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_LongtermPurchaseCommitmentWaterPurchased_41c18156-2447-4845-b7c1-21aaf833be1a" xlink:href="hto-20251231.xsd#hto_LongtermPurchaseCommitmentWaterPurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_LongtermPurchaseCommitmentWaterPurchased_41c18156-2447-4845-b7c1-21aaf833be1a" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermPurchaseCommitmentPeriod_689be5bf-ecda-408d-9004-88deb840caa4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermPurchaseCommitmentPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_us-gaap_LongtermPurchaseCommitmentPeriod_689be5bf-ecda-408d-9004-88deb840caa4" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_LongTermPurchaseCommitmentMinimumAcreFeetRequired_e103ad66-711b-43e0-bba7-2fd8838b8b95" xlink:href="hto-20251231.xsd#hto_LongTermPurchaseCommitmentMinimumAcreFeetRequired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_LongTermPurchaseCommitmentMinimumAcreFeetRequired_e103ad66-711b-43e0-bba7-2fd8838b8b95" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_NoticePeriodRequiredForContractAdjustment_e03657c0-9a4a-4428-9b33-b0b2c857f513" xlink:href="hto-20251231.xsd#hto_NoticePeriodRequiredForContractAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_NoticePeriodRequiredForContractAdjustment_e03657c0-9a4a-4428-9b33-b0b2c857f513" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ContractAgreementTerm_75b6a01e-5921-40ea-bd83-27fa407b6aba" xlink:href="hto-20251231.xsd#hto_ContractAgreementTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_ContractAgreementTerm_75b6a01e-5921-40ea-bd83-27fa407b6aba" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ContractAgreementRenewalTerm_019c421e-47b6-748d-9b21-4668b72a0f75" xlink:href="hto-20251231.xsd#hto_ContractAgreementRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_ContractAgreementRenewalTerm_019c421e-47b6-748d-9b21-4668b72a0f75" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_LongTermPurchaseCommitmentWholesaleDiscount_e721e633-c1c7-4e3e-8c0f-59b908e4d475" xlink:href="hto-20251231.xsd#hto_LongTermPurchaseCommitmentWholesaleDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_LongTermPurchaseCommitmentWholesaleDiscount_e721e633-c1c7-4e3e-8c0f-59b908e4d475" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_LongTermPurchaseCommitmentTariffRate_8b08592e-a83f-43d0-a81f-ae37d2005076" xlink:href="hto-20251231.xsd#hto_LongTermPurchaseCommitmentTariffRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_LongTermPurchaseCommitmentTariffRate_8b08592e-a83f-43d0-a81f-ae37d2005076" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityNumberOfEmployees_f7edd93d-7b1e-43fb-9e4d-18ee3e9af2b9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityNumberOfEmployees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_dei_EntityNumberOfEmployees_f7edd93d-7b1e-43fb-9e4d-18ee3e9af2b9" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_BargainingAgreementsTerm_8ea91e2d-dcc7-4316-ae00-009f62cbb6e5" xlink:href="hto-20251231.xsd#hto_BargainingAgreementsTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_BargainingAgreementsTerm_8ea91e2d-dcc7-4316-ae00-009f62cbb6e5" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CollectiveBargainingAgreementWageIncreasePercentYearOne_74a8f730-b546-43ee-beb2-39c276ec7278" xlink:href="hto-20251231.xsd#hto_CollectiveBargainingAgreementWageIncreasePercentYearOne"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_CollectiveBargainingAgreementWageIncreasePercentYearOne_74a8f730-b546-43ee-beb2-39c276ec7278" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CollectiveBargainingAgreementWageIncreasePercentYearTwo_8d034862-ec50-4a2c-9bb3-c66ba20e89f8" xlink:href="hto-20251231.xsd#hto_CollectiveBargainingAgreementWageIncreasePercentYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_CollectiveBargainingAgreementWageIncreasePercentYearTwo_8d034862-ec50-4a2c-9bb3-c66ba20e89f8" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CollectiveBargainingAgreementWageIncreasePercentYearThree_b93599b9-0001-48d4-af22-2f24b8a47a61" xlink:href="hto-20251231.xsd#hto_CollectiveBargainingAgreementWageIncreasePercentYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_7710a281-a0b2-4355-825d-9219c0ab988e" xlink:to="loc_hto_CollectiveBargainingAgreementWageIncreasePercentYearThree_b93599b9-0001-48d4-af22-2f24b8a47a61" xlink:type="arc" order="25"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/ContingenciesDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#ContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/ContingenciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_cf2fdb23-f37d-4b50-a5be-f38de8aeb8f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_edc2acdb-bc7b-4988-9667-34ddadadd278" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_cf2fdb23-f37d-4b50-a5be-f38de8aeb8f7" xlink:to="loc_us-gaap_LossContingenciesTable_edc2acdb-bc7b-4988-9667-34ddadadd278" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_e1e4e272-8ffa-44fb-b193-3ba3676d9615" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_edc2acdb-bc7b-4988-9667-34ddadadd278" xlink:to="loc_srt_ConsolidatedEntitiesAxis_e1e4e272-8ffa-44fb-b193-3ba3676d9615" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_e1e4e272-8ffa-44fb-b193-3ba3676d9615_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_e1e4e272-8ffa-44fb-b193-3ba3676d9615" xlink:to="loc_srt_ConsolidatedEntitiesDomain_e1e4e272-8ffa-44fb-b193-3ba3676d9615_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_17332898-0d7a-4e42-afa9-1cad0d057517" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_e1e4e272-8ffa-44fb-b193-3ba3676d9615" xlink:to="loc_srt_ConsolidatedEntitiesDomain_17332898-0d7a-4e42-afa9-1cad0d057517" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SanJoseWaterCompanyMember_019c53eb-924b-7010-b7cc-b8d3632992b1" xlink:href="hto-20251231.xsd#hto_SanJoseWaterCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_17332898-0d7a-4e42-afa9-1cad0d057517" xlink:to="loc_hto_SanJoseWaterCompanyMember_019c53eb-924b-7010-b7cc-b8d3632992b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ConnecticutWaterCompanyMember_019c53eb-b3ad-7b27-95b7-d73b236f55f2" xlink:href="hto-20251231.xsd#hto_ConnecticutWaterCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_17332898-0d7a-4e42-afa9-1cad0d057517" xlink:to="loc_hto_ConnecticutWaterCompanyMember_019c53eb-b3ad-7b27-95b7-d73b236f55f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_MaineWaterCompanyMember_019c53eb-cc16-7113-9dd3-e2bc8498bd42" xlink:href="hto-20251231.xsd#hto_MaineWaterCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_17332898-0d7a-4e42-afa9-1cad0d057517" xlink:to="loc_hto_MaineWaterCompanyMember_019c53eb-cc16-7113-9dd3-e2bc8498bd42" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLegalSettlements_e085d109-5d53-4dfb-b9fc-a618e65420f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromLegalSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_cf2fdb23-f37d-4b50-a5be-f38de8aeb8f7" xlink:to="loc_us-gaap_ProceedsFromLegalSettlements_e085d109-5d53-4dfb-b9fc-a618e65420f9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SettlementLiabilitiesCurrent_019c2d83-5053-77ec-90e0-94f482e8f22e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SettlementLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_cf2fdb23-f37d-4b50-a5be-f38de8aeb8f7" xlink:to="loc_us-gaap_SettlementLiabilitiesCurrent_019c2d83-5053-77ec-90e0-94f482e8f22e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_LossContingencyReceivableNoncurrentPeriod_eb98cbf0-62a8-4275-9dcf-775abab7fe43" xlink:href="hto-20251231.xsd#hto_LossContingencyReceivableNoncurrentPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_cf2fdb23-f37d-4b50-a5be-f38de8aeb8f7" xlink:to="loc_hto_LossContingencyReceivableNoncurrentPeriod_eb98cbf0-62a8-4275-9dcf-775abab7fe43" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/BenefitPlansNarrativeDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#BenefitPlansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/BenefitPlansNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_29c9f4df-0f53-41dc-b08c-a1aa90ce95da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_29c9f4df-0f53-41dc-b08c-a1aa90ce95da" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_e3cf0415-9c61-4f33-948e-c66d8d2b1dd7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_29c9f4df-0f53-41dc-b08c-a1aa90ce95da" xlink:to="loc_srt_TitleOfIndividualAxis_e3cf0415-9c61-4f33-948e-c66d8d2b1dd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_e3cf0415-9c61-4f33-948e-c66d8d2b1dd7_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_e3cf0415-9c61-4f33-948e-c66d8d2b1dd7" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_e3cf0415-9c61-4f33-948e-c66d8d2b1dd7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_1fd1ec88-f368-420c-a38d-08ffa1b2de0d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_e3cf0415-9c61-4f33-948e-c66d8d2b1dd7" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_1fd1ec88-f368-420c-a38d-08ffa1b2de0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_TWCEmployeesMember_019c780e-3cc8-7a74-8493-d42df657a75e" xlink:href="hto-20251231.xsd#hto_TWCEmployeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_1fd1ec88-f368-420c-a38d-08ffa1b2de0d" xlink:to="loc_hto_TWCEmployeesMember_019c780e-3cc8-7a74-8493-d42df657a75e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_CTWSEmployeesMember_019c3403-8b9a-718f-b8d4-183578e870d3" xlink:href="hto-20251231.xsd#hto_CTWSEmployeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_1fd1ec88-f368-420c-a38d-08ffa1b2de0d" xlink:to="loc_hto_CTWSEmployeesMember_019c3403-8b9a-718f-b8d4-183578e870d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ExecutivesAndNonEmployeeDirectorsMember_f64ea190-c93c-4b52-9f45-cc0d7466ee67" xlink:href="hto-20251231.xsd#hto_ExecutivesAndNonEmployeeDirectorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_1fd1ec88-f368-420c-a38d-08ffa1b2de0d" xlink:to="loc_hto_ExecutivesAndNonEmployeeDirectorsMember_f64ea190-c93c-4b52-9f45-cc0d7466ee67" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_b79d57ea-8d67-4d3b-824e-2c60efda60ee" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_29c9f4df-0f53-41dc-b08c-a1aa90ce95da" xlink:to="loc_srt_RangeAxis_b79d57ea-8d67-4d3b-824e-2c60efda60ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b79d57ea-8d67-4d3b-824e-2c60efda60ee_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_b79d57ea-8d67-4d3b-824e-2c60efda60ee" xlink:to="loc_srt_RangeMember_b79d57ea-8d67-4d3b-824e-2c60efda60ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_010de864-8c7f-434d-9af7-b27af433362d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_b79d57ea-8d67-4d3b-824e-2c60efda60ee" xlink:to="loc_srt_RangeMember_010de864-8c7f-434d-9af7-b27af433362d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_406812e0-0bb9-4761-b7a6-7656346495e6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_010de864-8c7f-434d-9af7-b27af433362d" xlink:to="loc_srt_MinimumMember_406812e0-0bb9-4761-b7a6-7656346495e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_17648bf5-d6c2-425f-8a0f-ee98caef39e4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_010de864-8c7f-434d-9af7-b27af433362d" xlink:to="loc_srt_MaximumMember_17648bf5-d6c2-425f-8a0f-ee98caef39e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_f0f72ac6-2e39-44c2-9ffd-2f0373fdaa26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_29c9f4df-0f53-41dc-b08c-a1aa90ce95da" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_f0f72ac6-2e39-44c2-9ffd-2f0373fdaa26" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_f0f72ac6-2e39-44c2-9ffd-2f0373fdaa26_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_f0f72ac6-2e39-44c2-9ffd-2f0373fdaa26" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_f0f72ac6-2e39-44c2-9ffd-2f0373fdaa26_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_d6a94aaf-e8ee-4c0a-8074-ddd6e1dd9cdb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_f0f72ac6-2e39-44c2-9ffd-2f0373fdaa26" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_d6a94aaf-e8ee-4c0a-8074-ddd6e1dd9cdb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_85520d86-f554-4059-b0b3-b0541187e5fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_d6a94aaf-e8ee-4c0a-8074-ddd6e1dd9cdb" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_85520d86-f554-4059-b0b3-b0541187e5fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember_6b7cf13a-72c9-47ce-9446-f2c335fd54c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_d6a94aaf-e8ee-4c0a-8074-ddd6e1dd9cdb" xlink:to="loc_us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember_6b7cf13a-72c9-47ce-9446-f2c335fd54c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_a830c0de-b7e3-49c7-a397-f5ba01ab3d8f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_29c9f4df-0f53-41dc-b08c-a1aa90ce95da" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_a830c0de-b7e3-49c7-a397-f5ba01ab3d8f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_a830c0de-b7e3-49c7-a397-f5ba01ab3d8f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_a830c0de-b7e3-49c7-a397-f5ba01ab3d8f" xlink:to="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_a830c0de-b7e3-49c7-a397-f5ba01ab3d8f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_e88c653b-9b47-425a-862d-b90870074599" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_a830c0de-b7e3-49c7-a397-f5ba01ab3d8f" xlink:to="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_e88c653b-9b47-425a-862d-b90870074599" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember_5930a4cf-1eda-4bb4-a23d-82cdde6a6df3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_e88c653b-9b47-425a-862d-b90870074599" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember_5930a4cf-1eda-4bb4-a23d-82cdde6a6df3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_2dcf39d6-dfa7-4701-b13c-2e2430f1b5d7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_29c9f4df-0f53-41dc-b08c-a1aa90ce95da" xlink:to="loc_srt_ConsolidatedEntitiesAxis_2dcf39d6-dfa7-4701-b13c-2e2430f1b5d7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_2dcf39d6-dfa7-4701-b13c-2e2430f1b5d7_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_2dcf39d6-dfa7-4701-b13c-2e2430f1b5d7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_2dcf39d6-dfa7-4701-b13c-2e2430f1b5d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_af12619a-b073-4cd8-871b-b3c0738a23e0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_2dcf39d6-dfa7-4701-b13c-2e2430f1b5d7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_af12619a-b073-4cd8-871b-b3c0738a23e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ConnecticutWaterCompanyMember_b8eb3c1f-cd70-43b9-b4b1-fed6676def5a" xlink:href="hto-20251231.xsd#hto_ConnecticutWaterCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_af12619a-b073-4cd8-871b-b3c0738a23e0" xlink:to="loc_hto_ConnecticutWaterCompanyMember_b8eb3c1f-cd70-43b9-b4b1-fed6676def5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetAxis_a9fbc6cb-a86a-41a8-ba38-7d1ca98e2522" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryAssetAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_29c9f4df-0f53-41dc-b08c-a1aa90ce95da" xlink:to="loc_us-gaap_RegulatoryAssetAxis_a9fbc6cb-a86a-41a8-ba38-7d1ca98e2522" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetDomain_a9fbc6cb-a86a-41a8-ba38-7d1ca98e2522_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RegulatoryAssetAxis_a9fbc6cb-a86a-41a8-ba38-7d1ca98e2522" xlink:to="loc_us-gaap_RegulatoryAssetDomain_a9fbc6cb-a86a-41a8-ba38-7d1ca98e2522_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetDomain_977d815b-3340-4ec3-a5a5-ed6a4217964f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RegulatoryAssetAxis_a9fbc6cb-a86a-41a8-ba38-7d1ca98e2522" xlink:to="loc_us-gaap_RegulatoryAssetDomain_977d815b-3340-4ec3-a5a5-ed6a4217964f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementPlansCostsMember_fb6a4749-49bc-49fa-a0f2-7c4856b845e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionAndOtherPostretirementPlansCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_977d815b-3340-4ec3-a5a5-ed6a4217964f" xlink:to="loc_us-gaap_PensionAndOtherPostretirementPlansCostsMember_fb6a4749-49bc-49fa-a0f2-7c4856b845e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityAxis_8b8d79e6-a213-463e-938f-2429499941a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryLiabilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_29c9f4df-0f53-41dc-b08c-a1aa90ce95da" xlink:to="loc_us-gaap_RegulatoryLiabilityAxis_8b8d79e6-a213-463e-938f-2429499941a7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityDomain_8b8d79e6-a213-463e-938f-2429499941a7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryLiabilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RegulatoryLiabilityAxis_8b8d79e6-a213-463e-938f-2429499941a7" xlink:to="loc_us-gaap_RegulatoryLiabilityDomain_8b8d79e6-a213-463e-938f-2429499941a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityDomain_c5e0d052-1a16-4403-8819-17e237297093" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegulatoryLiabilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RegulatoryLiabilityAxis_8b8d79e6-a213-463e-938f-2429499941a7" xlink:to="loc_us-gaap_RegulatoryLiabilityDomain_c5e0d052-1a16-4403-8819-17e237297093" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementPlansCostsMember_59301710-ca93-48f5-8a18-aff01581456a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionAndOtherPostretirementPlansCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryLiabilityDomain_c5e0d052-1a16-4403-8819-17e237297093" xlink:to="loc_us-gaap_PensionAndOtherPostretirementPlansCostsMember_59301710-ca93-48f5-8a18-aff01581456a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_DefinedBenefitPlanInterestCreditingRate_019c780f-4379-700b-90fa-1b7e6e6be95c" xlink:href="hto-20251231.xsd#hto_DefinedBenefitPlanInterestCreditingRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_hto_DefinedBenefitPlanInterestCreditingRate_019c780f-4379-700b-90fa-1b7e6e6be95c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationWeightedAverageInterestCreditingRate_019c780c-7797-75c0-9edf-3d535b0180fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationWeightedAverageInterestCreditingRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationWeightedAverageInterestCreditingRate_019c780c-7797-75c0-9edf-3d535b0180fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_DefinedBenefitPlanRateOfCompensationIncrease_f01763d5-4046-47e7-8723-5afebcf4fe00" xlink:href="hto-20251231.xsd#hto_DefinedBenefitPlanRateOfCompensationIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_hto_DefinedBenefitPlanRateOfCompensationIncrease_f01763d5-4046-47e7-8723-5afebcf4fe00" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_DefinedBenefitPlanPeriodForPerformanceStandards_b3247e44-f2ff-433b-a043-7eef8b28caea" xlink:href="hto-20251231.xsd#hto_DefinedBenefitPlanPeriodForPerformanceStandards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_hto_DefinedBenefitPlanPeriodForPerformanceStandards_b3247e44-f2ff-433b-a043-7eef8b28caea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets_0ff7ca39-debc-4f0c-83e7-cc4b6260c45e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets_0ff7ca39-debc-4f0c-83e7-cc4b6260c45e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanBenefitObligation_47beb94a-af39-4a63-83e9-473a38821f60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanBenefitObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_DefinedBenefitPlanBenefitObligation_47beb94a-af39-4a63-83e9-473a38821f60" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_1d6aa31c-59c3-4322-9462-a12ac4447b1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_1d6aa31c-59c3-4322-9462-a12ac4447b1e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent_2d426270-5e61-481d-872d-608c8e6f113f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent_2d426270-5e61-481d-872d-608c8e6f113f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_b62474a9-9b80-4ad6-bc5b-66b23e1fa294" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanContributionsByEmployer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_b62474a9-9b80-4ad6-bc5b-66b23e1fa294" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashSurrenderValueOfLifeInsurance_ebdf1090-d9f6-4b4f-9a08-539f783e23d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashSurrenderValueOfLifeInsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_CashSurrenderValueOfLifeInsurance_ebdf1090-d9f6-4b4f-9a08-539f783e23d6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_HealthCareSpendingAccountAnnualMaximumEmployeeContribution_246c879e-451d-4efb-9d15-b6c8d521d69f" xlink:href="hto-20251231.xsd#hto_HealthCareSpendingAccountAnnualMaximumEmployeeContribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_hto_HealthCareSpendingAccountAnnualMaximumEmployeeContribution_246c879e-451d-4efb-9d15-b6c8d521d69f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_DependentCareSpendingAccountAnnualMaximumEmployeeContribution_2d80e3b6-c0a8-40d5-9fe1-42928baf37f4" xlink:href="hto-20251231.xsd#hto_DependentCareSpendingAccountAnnualMaximumEmployeeContribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_hto_DependentCareSpendingAccountAnnualMaximumEmployeeContribution_2d80e3b6-c0a8-40d5-9fe1-42928baf37f4" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer_f97e6d6e-22fe-41e7-a373-c02e000c0e2f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer_f97e6d6e-22fe-41e7-a373-c02e000c0e2f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_DeferredCompensationArrangementWithIndividualDeferralAmount_ca60c1b5-17ed-4eb0-94ae-501730749274" xlink:href="hto-20251231.xsd#hto_DeferredCompensationArrangementWithIndividualDeferralAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_hto_DeferredCompensationArrangementWithIndividualDeferralAmount_ca60c1b5-17ed-4eb0-94ae-501730749274" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear_5932cb65-5644-4f29-a2a9-2b0fd0628072" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear_5932cb65-5644-4f29-a2a9-2b0fd0628072" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate1_47407430-0608-4d4c-b099-160da9c76870" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate1_47407430-0608-4d4c-b099-160da9c76870" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_DefinedBenefitPlanActuarialGainLossDiscountRateChange_cf7b6114-a3b7-42f2-9ad4-041845eec352" xlink:href="hto-20251231.xsd#hto_DefinedBenefitPlanActuarialGainLossDiscountRateChange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_hto_DefinedBenefitPlanActuarialGainLossDiscountRateChange_cf7b6114-a3b7-42f2-9ad4-041845eec352" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_DefinedBenefitPlanActuarialGainLossDataAndOtherChanges_b62c4f8e-ee32-44e6-964e-472099ac60e4" xlink:href="hto-20251231.xsd#hto_DefinedBenefitPlanActuarialGainLossDataAndOtherChanges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_hto_DefinedBenefitPlanActuarialGainLossDataAndOtherChanges_b62c4f8e-ee32-44e6-964e-472099ac60e4" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation_005a449b-b07e-4a91-a610-a61f55ea92a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation_005a449b-b07e-4a91-a610-a61f55ea92a4" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RegulatoryAssetsFundedStatusOfObligation_07820362-575a-465a-8748-49ffe355ecfb" xlink:href="hto-20251231.xsd#hto_RegulatoryAssetsFundedStatusOfObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_hto_RegulatoryAssetsFundedStatusOfObligation_07820362-575a-465a-8748-49ffe355ecfb" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RegulatoryLiabilitiesAccruedBenefitCost_48f0d588-321a-4415-9df6-4b21bbd4d2ee" xlink:href="hto-20251231.xsd#hto_RegulatoryLiabilitiesAccruedBenefitCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_hto_RegulatoryLiabilitiesAccruedBenefitCost_48f0d588-321a-4415-9df6-4b21bbd4d2ee" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax_5f37cb81-d3a6-42d5-89b6-bc15ec17bc76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax_5f37cb81-d3a6-42d5-89b6-bc15ec17bc76" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostsCreditArisingDuringPeriodNetOfTax_7ce5f8d5-e606-4571-9042-6e4054249d1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostsCreditArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostsCreditArisingDuringPeriodNetOfTax_7ce5f8d5-e606-4571-9042-6e4054249d1b" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_291f22bb-0bfc-436a-a1c6-e837f137464f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_5931a825-7357-4694-8f1d-8e82a678458d" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_291f22bb-0bfc-436a-a1c6-e837f137464f" xlink:type="arc" order="23"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/BenefitPlansScheduleofFairValueofPlanAssetsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#BenefitPlansScheduleofFairValueofPlanAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/BenefitPlansScheduleofFairValueofPlanAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fdf17bd1-280f-4b73-bab5-d842d09f71dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_cf15d1fa-131f-45a3-91e0-9b3e244f2113" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fdf17bd1-280f-4b73-bab5-d842d09f71dd" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_cf15d1fa-131f-45a3-91e0-9b3e244f2113" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_94585c1e-3a14-4c80-b006-a041af595dfe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_cf15d1fa-131f-45a3-91e0-9b3e244f2113" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_94585c1e-3a14-4c80-b006-a041af595dfe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_94585c1e-3a14-4c80-b006-a041af595dfe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_94585c1e-3a14-4c80-b006-a041af595dfe" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_94585c1e-3a14-4c80-b006-a041af595dfe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_895156c5-1d9a-46c9-9a3a-a23b990042b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_94585c1e-3a14-4c80-b006-a041af595dfe" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_895156c5-1d9a-46c9-9a3a-a23b990042b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember_691a4bbc-b433-47dd-a6c4-e7870a7d238b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_895156c5-1d9a-46c9-9a3a-a23b990042b6" xlink:to="loc_us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember_691a4bbc-b433-47dd-a6c4-e7870a7d238b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_9dd3c044-74a7-432e-9aa3-4fc4052be4ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_cf15d1fa-131f-45a3-91e0-9b3e244f2113" xlink:to="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_9dd3c044-74a7-432e-9aa3-4fc4052be4ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_9dd3c044-74a7-432e-9aa3-4fc4052be4ba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_9dd3c044-74a7-432e-9aa3-4fc4052be4ba" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_9dd3c044-74a7-432e-9aa3-4fc4052be4ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_7757cb11-a80f-4f21-ae20-1c9175f0803d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_9dd3c044-74a7-432e-9aa3-4fc4052be4ba" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_7757cb11-a80f-4f21-ae20-1c9175f0803d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_02927dd1-683b-48a1-b99e-60a8493a471a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_7757cb11-a80f-4f21-ae20-1c9175f0803d" xlink:to="loc_us-gaap_MoneyMarketFundsMember_02927dd1-683b-48a1-b99e-60a8493a471a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MutualFundMember_6546dbe5-994c-4a0e-a812-9274316f1842" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MutualFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_7757cb11-a80f-4f21-ae20-1c9175f0803d" xlink:to="loc_us-gaap_MutualFundMember_6546dbe5-994c-4a0e-a812-9274316f1842" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedIncomeFundsMember_f4c93c1b-6fc1-4b58-9357-f533a77d92cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FixedIncomeFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_7757cb11-a80f-4f21-ae20-1c9175f0803d" xlink:to="loc_us-gaap_FixedIncomeFundsMember_f4c93c1b-6fc1-4b58-9357-f533a77d92cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_c868a353-798a-42dd-9d20-b7d566da92a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_cf15d1fa-131f-45a3-91e0-9b3e244f2113" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_c868a353-798a-42dd-9d20-b7d566da92a0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c868a353-798a-42dd-9d20-b7d566da92a0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_c868a353-798a-42dd-9d20-b7d566da92a0" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c868a353-798a-42dd-9d20-b7d566da92a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4e1ff1b1-77cd-4db9-9b8f-9433357feb05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_c868a353-798a-42dd-9d20-b7d566da92a0" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4e1ff1b1-77cd-4db9-9b8f-9433357feb05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_93490c72-d8ca-4b24-8b92-f1c88a432a84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4e1ff1b1-77cd-4db9-9b8f-9433357feb05" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_93490c72-d8ca-4b24-8b92-f1c88a432a84" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_34cb1368-a14e-43d0-97c6-402e80bbbf52" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4e1ff1b1-77cd-4db9-9b8f-9433357feb05" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_34cb1368-a14e-43d0-97c6-402e80bbbf52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_7439f4c4-02d0-4c5c-af2f-bdc3f702d4cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4e1ff1b1-77cd-4db9-9b8f-9433357feb05" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_7439f4c4-02d0-4c5c-af2f-bdc3f702d4cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_89fb0e18-50da-49de-aa9b-761d8be5f8f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fdf17bd1-280f-4b73-bab5-d842d09f71dd" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_89fb0e18-50da-49de-aa9b-761d8be5f8f1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/BenefitPlansScheduleofActuarialCalculationAssumptionsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#BenefitPlansScheduleofActuarialCalculationAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/BenefitPlansScheduleofActuarialCalculationAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b0937fed-11b8-45fd-bccc-0c0c5cf79303" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_d85c4b84-3e14-4c04-a822-0275a33533db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b0937fed-11b8-45fd-bccc-0c0c5cf79303" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_d85c4b84-3e14-4c04-a822-0275a33533db" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_26882a9a-12c2-45b6-9c42-8a0eaa5e4013" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_d85c4b84-3e14-4c04-a822-0275a33533db" xlink:to="loc_srt_RangeAxis_26882a9a-12c2-45b6-9c42-8a0eaa5e4013" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_26882a9a-12c2-45b6-9c42-8a0eaa5e4013_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_26882a9a-12c2-45b6-9c42-8a0eaa5e4013" xlink:to="loc_srt_RangeMember_26882a9a-12c2-45b6-9c42-8a0eaa5e4013_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b49b2b4f-8377-4184-8c74-4530b8085176" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_26882a9a-12c2-45b6-9c42-8a0eaa5e4013" xlink:to="loc_srt_RangeMember_b49b2b4f-8377-4184-8c74-4530b8085176" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_39e0ab3f-5a5a-46b3-8423-e8b7050318f0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b49b2b4f-8377-4184-8c74-4530b8085176" xlink:to="loc_srt_MinimumMember_39e0ab3f-5a5a-46b3-8423-e8b7050318f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_484a01cb-2283-4602-b5d1-9b0055ac1ff3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b49b2b4f-8377-4184-8c74-4530b8085176" xlink:to="loc_srt_MaximumMember_484a01cb-2283-4602-b5d1-9b0055ac1ff3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_4016304e-2c07-47de-8800-d477a6d09401" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_d85c4b84-3e14-4c04-a822-0275a33533db" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_4016304e-2c07-47de-8800-d477a6d09401" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_4016304e-2c07-47de-8800-d477a6d09401_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_4016304e-2c07-47de-8800-d477a6d09401" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_4016304e-2c07-47de-8800-d477a6d09401_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_d6154c3b-a6e4-4717-8ad4-767d6ee677e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_4016304e-2c07-47de-8800-d477a6d09401" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_d6154c3b-a6e4-4717-8ad4-767d6ee677e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_1c209b27-c217-4c0e-b49f-dc83f0d7352c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_d6154c3b-a6e4-4717-8ad4-767d6ee677e8" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_1c209b27-c217-4c0e-b49f-dc83f0d7352c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_6fc5407a-a80c-419f-b68d-53e4ab4bdc9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_d6154c3b-a6e4-4717-8ad4-767d6ee677e8" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_6fc5407a-a80c-419f-b68d-53e4ab4bdc9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate_59031645-3264-4656-a046-b2137e3bc933" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b0937fed-11b8-45fd-bccc-0c0c5cf79303" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate_59031645-3264-4656-a046-b2137e3bc933" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets_7b6c07ed-d38f-4cfe-8254-75acc71b9bbf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b0937fed-11b8-45fd-bccc-0c0c5cf79303" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets_7b6c07ed-d38f-4cfe-8254-75acc71b9bbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease_5ed6675d-8991-4be7-83fa-85422f13d6bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b0937fed-11b8-45fd-bccc-0c0c5cf79303" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease_5ed6675d-8991-4be7-83fa-85422f13d6bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate_7ebd5638-7448-4dc1-9e2a-1803a45e3275" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b0937fed-11b8-45fd-bccc-0c0c5cf79303" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate_7ebd5638-7448-4dc1-9e2a-1803a45e3275" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease_dd6a7649-c8a8-43fe-b43a-10860ae06fbb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b0937fed-11b8-45fd-bccc-0c0c5cf79303" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease_dd6a7649-c8a8-43fe-b43a-10860ae06fbb" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/BenefitPlansScheduleofNetPeriodicBenefitCostDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#BenefitPlansScheduleofNetPeriodicBenefitCostDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/BenefitPlansScheduleofNetPeriodicBenefitCostDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fa47cfc2-455f-49df-a804-bad743b79463" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_c7ea5250-3ec4-4298-9587-fedecac4fcde" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fa47cfc2-455f-49df-a804-bad743b79463" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_c7ea5250-3ec4-4298-9587-fedecac4fcde" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_97e18c5e-4319-4289-afa6-515505f459d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_c7ea5250-3ec4-4298-9587-fedecac4fcde" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_97e18c5e-4319-4289-afa6-515505f459d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_97e18c5e-4319-4289-afa6-515505f459d7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_97e18c5e-4319-4289-afa6-515505f459d7" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_97e18c5e-4319-4289-afa6-515505f459d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_7a38347d-e738-4ef6-8ddc-fcbf6442e15e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_97e18c5e-4319-4289-afa6-515505f459d7" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_7a38347d-e738-4ef6-8ddc-fcbf6442e15e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_d99c5879-1025-41e9-987e-73729095d7a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_7a38347d-e738-4ef6-8ddc-fcbf6442e15e" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_d99c5879-1025-41e9-987e-73729095d7a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_61c4f8fd-e4db-45a6-9acd-f5f4ccb7207f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_7a38347d-e738-4ef6-8ddc-fcbf6442e15e" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_61c4f8fd-e4db-45a6-9acd-f5f4ccb7207f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_0feefe3e-3165-4719-949b-dca8a6970ad6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fa47cfc2-455f-49df-a804-bad743b79463" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_0feefe3e-3165-4719-949b-dca8a6970ad6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_35a78606-f63e-44b7-a7f6-6c75e5912e86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fa47cfc2-455f-49df-a804-bad743b79463" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_35a78606-f63e-44b7-a7f6-6c75e5912e86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_61fe4488-0726-4eda-9565-29eb8ac2b2fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fa47cfc2-455f-49df-a804-bad743b79463" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_61fe4488-0726-4eda-9565-29eb8ac2b2fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_b1d3f41f-f507-41f6-b122-eb9929f91308" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fa47cfc2-455f-49df-a804-bad743b79463" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_b1d3f41f-f507-41f6-b122-eb9929f91308" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit_23f1714b-7057-41b2-949f-e3937751732a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fa47cfc2-455f-49df-a804-bad743b79463" xlink:to="loc_us-gaap_DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit_23f1714b-7057-41b2-949f-e3937751732a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanOtherCosts_d0659246-c070-46d1-b792-6180cdab5c1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanOtherCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fa47cfc2-455f-49df-a804-bad743b79463" xlink:to="loc_us-gaap_DefinedBenefitPlanOtherCosts_d0659246-c070-46d1-b792-6180cdab5c1d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_63e2a40d-2834-4861-8ca7-70dcb4a7f288" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_fa47cfc2-455f-49df-a804-bad743b79463" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_63e2a40d-2834-4861-8ca7-70dcb4a7f288" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/BenefitPlansScheduleofReconciliationofFundedStatusDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#BenefitPlansScheduleofReconciliationofFundedStatusDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/BenefitPlansScheduleofReconciliationofFundedStatusDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_abb1ece1-809a-49ab-a1e5-cffb0994f281" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_c0a66e96-36a5-4475-895c-726c99b83f18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_abb1ece1-809a-49ab-a1e5-cffb0994f281" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_c0a66e96-36a5-4475-895c-726c99b83f18" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_118e6268-f52a-4044-9a0d-c531d8b92a90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_c0a66e96-36a5-4475-895c-726c99b83f18" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_118e6268-f52a-4044-9a0d-c531d8b92a90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_118e6268-f52a-4044-9a0d-c531d8b92a90_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_118e6268-f52a-4044-9a0d-c531d8b92a90" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_118e6268-f52a-4044-9a0d-c531d8b92a90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_c3a596b7-b991-40ef-b4c3-68dd42611431" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_118e6268-f52a-4044-9a0d-c531d8b92a90" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_c3a596b7-b991-40ef-b4c3-68dd42611431" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_cbe63f73-329f-486d-948e-e4c0e5df7e58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_c3a596b7-b991-40ef-b4c3-68dd42611431" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_cbe63f73-329f-486d-948e-e4c0e5df7e58" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_38bdcebe-7a63-48f9-8ebc-63d8e5b06444" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_c3a596b7-b991-40ef-b4c3-68dd42611431" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_38bdcebe-7a63-48f9-8ebc-63d8e5b06444" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_93dd0bf3-c7b9-432c-80e1-4acd599c0b85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_abb1ece1-809a-49ab-a1e5-cffb0994f281" xlink:to="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_93dd0bf3-c7b9-432c-80e1-4acd599c0b85" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanBenefitObligation_8e9d8293-d88e-465a-823f-d2b62169ddb7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanBenefitObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_93dd0bf3-c7b9-432c-80e1-4acd599c0b85" xlink:to="loc_us-gaap_DefinedBenefitPlanBenefitObligation_8e9d8293-d88e-465a-823f-d2b62169ddb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_5834e417-d3db-4b43-b9f1-8bd5d9b29f03" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_93dd0bf3-c7b9-432c-80e1-4acd599c0b85" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_5834e417-d3db-4b43-b9f1-8bd5d9b29f03" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_e020110b-57f9-4a5f-a9b3-48d9bac0c662" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_93dd0bf3-c7b9-432c-80e1-4acd599c0b85" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_e020110b-57f9-4a5f-a9b3-48d9bac0c662" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActuarialGainLoss_828300e6-1f5a-4156-96b2-83d635a642ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanActuarialGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_93dd0bf3-c7b9-432c-80e1-4acd599c0b85" xlink:to="loc_us-gaap_DefinedBenefitPlanActuarialGainLoss_828300e6-1f5a-4156-96b2-83d635a642ce" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_DefinedBenefitPlanImplicitRateSubsidy_75e3d682-1009-4cfb-ac82-c083387644a4" xlink:href="hto-20251231.xsd#hto_DefinedBenefitPlanImplicitRateSubsidy"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_93dd0bf3-c7b9-432c-80e1-4acd599c0b85" xlink:to="loc_hto_DefinedBenefitPlanImplicitRateSubsidy_75e3d682-1009-4cfb-ac82-c083387644a4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanBenefitObligationContributionsByPlanParticipant_5d1e150b-aaf4-431b-8e41-640ee9a3d3f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanBenefitObligationContributionsByPlanParticipant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_93dd0bf3-c7b9-432c-80e1-4acd599c0b85" xlink:to="loc_us-gaap_DefinedBenefitPlanBenefitObligationContributionsByPlanParticipant_5d1e150b-aaf4-431b-8e41-640ee9a3d3f7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanOtherChanges_7a333b85-c2d6-4f65-802a-595dc612ba31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanOtherChanges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_93dd0bf3-c7b9-432c-80e1-4acd599c0b85" xlink:to="loc_us-gaap_DefinedBenefitPlanOtherChanges_7a333b85-c2d6-4f65-802a-595dc612ba31" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanBenefitObligationBenefitsPaid_bbfa2a36-c995-4ae6-aeb0-4e8e6a93fcb8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanBenefitObligationBenefitsPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward_93dd0bf3-c7b9-432c-80e1-4acd599c0b85" xlink:to="loc_us-gaap_DefinedBenefitPlanBenefitObligationBenefitsPaid_bbfa2a36-c995-4ae6-aeb0-4e8e6a93fcb8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanBenefitObligation_659ae3c9-5d1d-42b3-97f1-a45240d23f52" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanBenefitObligation"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_a6dcae97-c918-42fd-9017-66de2e6ffb58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_abb1ece1-809a-49ab-a1e5-cffb0994f281" xlink:to="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_a6dcae97-c918-42fd-9017-66de2e6ffb58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_e861ad6b-0e39-452c-847a-a9ea746e1945" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_a6dcae97-c918-42fd-9017-66de2e6ffb58" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_e861ad6b-0e39-452c-847a-a9ea746e1945" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets_282b3699-bffd-442d-9940-d934a7ed391c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_a6dcae97-c918-42fd-9017-66de2e6ffb58" xlink:to="loc_us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets_282b3699-bffd-442d-9940-d934a7ed391c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_baace53d-4583-4655-a799-b94b0c44ab3c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanContributionsByEmployer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_a6dcae97-c918-42fd-9017-66de2e6ffb58" xlink:to="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_baace53d-4583-4655-a799-b94b0c44ab3c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsContributionsByPlanParticipant_69859704-a52f-4ec2-998c-ae591d353463" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPlanAssetsContributionsByPlanParticipant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_a6dcae97-c918-42fd-9017-66de2e6ffb58" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsContributionsByPlanParticipant_69859704-a52f-4ec2-998c-ae591d353463" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAdministrationExpenses_d21aa994-ba2b-4aca-a6ec-a092a23d1e91" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAdministrationExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_a6dcae97-c918-42fd-9017-66de2e6ffb58" xlink:to="loc_us-gaap_DefinedBenefitPlanAdministrationExpenses_d21aa994-ba2b-4aca-a6ec-a092a23d1e91" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid_3234cc0f-11ec-42aa-a016-2f7736b480d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward_a6dcae97-c918-42fd-9017-66de2e6ffb58" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid_3234cc0f-11ec-42aa-a016-2f7736b480d6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_ed3b0258-c939-4305-8d6a-81a1aecf4347" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_d7489081-27f2-4f4a-b460-db635b07f4ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFundedStatusOfPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_abb1ece1-809a-49ab-a1e5-cffb0994f281" xlink:to="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_d7489081-27f2-4f4a-b460-db635b07f4ec" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/BenefitPlansScheduleofAmountsRecognizedinBalanceSheetDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#BenefitPlansScheduleofAmountsRecognizedinBalanceSheetDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/BenefitPlansScheduleofAmountsRecognizedinBalanceSheetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b2154223-c4bd-435a-83d5-bfe04c114989" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_0247fc10-17a5-4edf-824f-3d8abb77afd9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b2154223-c4bd-435a-83d5-bfe04c114989" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_0247fc10-17a5-4edf-824f-3d8abb77afd9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_e70de1e8-395f-4b05-869f-0a5ebe47998e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_0247fc10-17a5-4edf-824f-3d8abb77afd9" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_e70de1e8-395f-4b05-869f-0a5ebe47998e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_e70de1e8-395f-4b05-869f-0a5ebe47998e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_e70de1e8-395f-4b05-869f-0a5ebe47998e" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_e70de1e8-395f-4b05-869f-0a5ebe47998e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_fd7450f7-1d47-4e41-9769-0e35911594ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_e70de1e8-395f-4b05-869f-0a5ebe47998e" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_fd7450f7-1d47-4e41-9769-0e35911594ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_48ead38f-5797-4116-8914-7e22d1b66745" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_fd7450f7-1d47-4e41-9769-0e35911594ba" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_48ead38f-5797-4116-8914-7e22d1b66745" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_4992d33e-cc74-4c11-a8e8-11aa94838bb2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_fd7450f7-1d47-4e41-9769-0e35911594ba" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_4992d33e-cc74-4c11-a8e8-11aa94838bb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent_78e4730c-7e1c-42b0-9891-33202feb975c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b2154223-c4bd-435a-83d5-bfe04c114989" xlink:to="loc_us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent_78e4730c-7e1c-42b0-9891-33202feb975c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities_dfecb784-559e-493a-bc13-1d48cb965fcc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b2154223-c4bd-435a-83d5-bfe04c114989" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities_dfecb784-559e-493a-bc13-1d48cb965fcc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_a6d7eaf6-0cd8-42fb-821b-0fd3d2d1e516" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b2154223-c4bd-435a-83d5-bfe04c114989" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_a6d7eaf6-0cd8-42fb-821b-0fd3d2d1e516" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet_ea1bcbbe-ba48-48dc-ab54-a01d39bb2af5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b2154223-c4bd-435a-83d5-bfe04c114989" xlink:to="loc_us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet_ea1bcbbe-ba48-48dc-ab54-a01d39bb2af5" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/BenefitPlansScheduleofAccumulatedandProjectedBenefitObligationsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#BenefitPlansScheduleofAccumulatedandProjectedBenefitObligationsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/BenefitPlansScheduleofAccumulatedandProjectedBenefitObligationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_be8c36dd-5c74-4795-8c2c-63c260f7c15a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_b0764320-f83d-4102-96ca-b6edad205f37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_be8c36dd-5c74-4795-8c2c-63c260f7c15a" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_b0764320-f83d-4102-96ca-b6edad205f37" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_5439592f-010b-4ea4-a718-1e65671835dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_b0764320-f83d-4102-96ca-b6edad205f37" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_5439592f-010b-4ea4-a718-1e65671835dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_5439592f-010b-4ea4-a718-1e65671835dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_5439592f-010b-4ea4-a718-1e65671835dc" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_5439592f-010b-4ea4-a718-1e65671835dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_6482d66a-0568-4f6c-b9b0-8b43a00e70a9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_5439592f-010b-4ea4-a718-1e65671835dc" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_6482d66a-0568-4f6c-b9b0-8b43a00e70a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_f1acca8d-9a76-46e4-9cb4-d1cddf67f145" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_6482d66a-0568-4f6c-b9b0-8b43a00e70a9" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_f1acca8d-9a76-46e4-9cb4-d1cddf67f145" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_5a93a304-9f57-4fa5-b7d8-9d4ef7be967e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_6482d66a-0568-4f6c-b9b0-8b43a00e70a9" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_5a93a304-9f57-4fa5-b7d8-9d4ef7be967e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAbstract_8f58433b-3797-46ec-9326-f24b0399d380" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_be8c36dd-5c74-4795-8c2c-63c260f7c15a" xlink:to="loc_us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAbstract_8f58433b-3797-46ec-9326-f24b0399d380" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPensionPlanWithProjectedBenefitObligationInExcessOfPlanAssetsProjectedBenefitObligation_e68596b9-bcca-4b53-b1d9-9da6f25f020e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPensionPlanWithProjectedBenefitObligationInExcessOfPlanAssetsProjectedBenefitObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAbstract_8f58433b-3797-46ec-9326-f24b0399d380" xlink:to="loc_us-gaap_DefinedBenefitPlanPensionPlanWithProjectedBenefitObligationInExcessOfPlanAssetsProjectedBenefitObligation_e68596b9-bcca-4b53-b1d9-9da6f25f020e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPensionPlanWithProjectedBenefitObligationInExcessOfPlanAssetsPlanAssets_8d4e8e10-2806-4fce-a6b5-305446afdf62" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPensionPlanWithProjectedBenefitObligationInExcessOfPlanAssetsPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAbstract_8f58433b-3797-46ec-9326-f24b0399d380" xlink:to="loc_us-gaap_DefinedBenefitPlanPensionPlanWithProjectedBenefitObligationInExcessOfPlanAssetsPlanAssets_8d4e8e10-2806-4fce-a6b5-305446afdf62" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAbstract_172b621b-8466-4f58-b6c8-402d74c14513" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_be8c36dd-5c74-4795-8c2c-63c260f7c15a" xlink:to="loc_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAbstract_172b621b-8466-4f58-b6c8-402d74c14513" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateAccumulatedBenefitObligation_b2697413-40eb-4b69-99de-97c15eeb1641" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateAccumulatedBenefitObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAbstract_172b621b-8466-4f58-b6c8-402d74c14513" xlink:to="loc_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateAccumulatedBenefitObligation_b2697413-40eb-4b69-99de-97c15eeb1641" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets_edddf392-92f0-4062-ac52-fa690d304a0c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAbstract_172b621b-8466-4f58-b6c8-402d74c14513" xlink:to="loc_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets_edddf392-92f0-4062-ac52-fa690d304a0c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/BenefitPlansScheduleofPlanAssetsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#BenefitPlansScheduleofPlanAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/BenefitPlansScheduleofPlanAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0a174621-2a08-4ce7-ae67-db40824387fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_96218395-d9ce-4c75-934d-9e5b1508223b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0a174621-2a08-4ce7-ae67-db40824387fb" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_96218395-d9ce-4c75-934d-9e5b1508223b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_947ed281-2e97-41ac-b755-58445be87b36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_96218395-d9ce-4c75-934d-9e5b1508223b" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_947ed281-2e97-41ac-b755-58445be87b36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_947ed281-2e97-41ac-b755-58445be87b36_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_947ed281-2e97-41ac-b755-58445be87b36" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_947ed281-2e97-41ac-b755-58445be87b36_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_48fa1a95-525a-4bad-8f90-697075de464d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_947ed281-2e97-41ac-b755-58445be87b36" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_48fa1a95-525a-4bad-8f90-697075de464d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_a2944718-1510-4925-a6a3-bdea82ba9b82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_48fa1a95-525a-4bad-8f90-697075de464d" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_a2944718-1510-4925-a6a3-bdea82ba9b82" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_1785b064-7c29-4e7a-95dc-a27df7de7085" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_48fa1a95-525a-4bad-8f90-697075de464d" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_1785b064-7c29-4e7a-95dc-a27df7de7085" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8e028491-7664-4b23-871d-d5161728957b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_96218395-d9ce-4c75-934d-9e5b1508223b" xlink:to="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8e028491-7664-4b23-871d-d5161728957b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_8e028491-7664-4b23-871d-d5161728957b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8e028491-7664-4b23-871d-d5161728957b" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_8e028491-7664-4b23-871d-d5161728957b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_400e6149-f281-487d-86ac-6c5b477fddef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8e028491-7664-4b23-871d-d5161728957b" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_400e6149-f281-487d-86ac-6c5b477fddef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDebtSecurityMember_b80bed48-b98c-4873-86fb-69e62f5a74e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDebtSecurityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_400e6149-f281-487d-86ac-6c5b477fddef" xlink:to="loc_us-gaap_DefinedBenefitPlanDebtSecurityMember_b80bed48-b98c-4873-86fb-69e62f5a74e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_4e84f699-d030-4eec-be5f-a3d285b1902a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanEquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_400e6149-f281-487d-86ac-6c5b477fddef" xlink:to="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_4e84f699-d030-4eec-be5f-a3d285b1902a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_214aec3c-968d-4edd-81c0-78c901ff593d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_400e6149-f281-487d-86ac-6c5b477fddef" xlink:to="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_214aec3c-968d-4edd-81c0-78c901ff593d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedIncomeSecuritiesMember_548b3664-89c3-4e73-ae7f-258e5cac09e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FixedIncomeSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_400e6149-f281-487d-86ac-6c5b477fddef" xlink:to="loc_us-gaap_FixedIncomeSecuritiesMember_548b3664-89c3-4e73-ae7f-258e5cac09e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_9e3016c0-1d30-4bb6-9c69-00c95ac0a624" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_96218395-d9ce-4c75-934d-9e5b1508223b" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_9e3016c0-1d30-4bb6-9c69-00c95ac0a624" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9e3016c0-1d30-4bb6-9c69-00c95ac0a624_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_9e3016c0-1d30-4bb6-9c69-00c95ac0a624" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9e3016c0-1d30-4bb6-9c69-00c95ac0a624_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7b12cb62-e154-4392-b26d-8dbb2bf1909a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_9e3016c0-1d30-4bb6-9c69-00c95ac0a624" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7b12cb62-e154-4392-b26d-8dbb2bf1909a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_b8d8a595-91e6-45d0-b76a-7fa68959719f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7b12cb62-e154-4392-b26d-8dbb2bf1909a" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_b8d8a595-91e6-45d0-b76a-7fa68959719f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_3644364b-a284-4349-b02f-9e7aa66f1e19" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7b12cb62-e154-4392-b26d-8dbb2bf1909a" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_3644364b-a284-4349-b02f-9e7aa66f1e19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_907ae833-bc3a-4a0f-a99f-5e365216ed48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7b12cb62-e154-4392-b26d-8dbb2bf1909a" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_907ae833-bc3a-4a0f-a99f-5e365216ed48" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_096dd97d-8152-4246-adb4-fbd779651e3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0a174621-2a08-4ce7-ae67-db40824387fb" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_096dd97d-8152-4246-adb4-fbd779651e3e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations_e325d27d-755c-49f4-8c94-c2fe58f9daa1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0a174621-2a08-4ce7-ae67-db40824387fb" xlink:to="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations_e325d27d-755c-49f4-8c94-c2fe58f9daa1" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/BenefitPlansScheduleofBenefitsExpectedtobePaidinNextFiveYearsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#BenefitPlansScheduleofBenefitsExpectedtobePaidinNextFiveYearsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/BenefitPlansScheduleofBenefitsExpectedtobePaidinNextFiveYearsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a0b86feb-a564-4fa0-adfb-805225c8114a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_4757ffc3-9dad-4b60-9dd4-d2ca91b6fd61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a0b86feb-a564-4fa0-adfb-805225c8114a" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_4757ffc3-9dad-4b60-9dd4-d2ca91b6fd61" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_c7398cbe-f4ec-4863-a74b-b7b01d23244d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_4757ffc3-9dad-4b60-9dd4-d2ca91b6fd61" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_c7398cbe-f4ec-4863-a74b-b7b01d23244d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_c7398cbe-f4ec-4863-a74b-b7b01d23244d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_c7398cbe-f4ec-4863-a74b-b7b01d23244d" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_c7398cbe-f4ec-4863-a74b-b7b01d23244d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_9fb531bb-0207-4e63-9527-2b77f8fc0c78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_c7398cbe-f4ec-4863-a74b-b7b01d23244d" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_9fb531bb-0207-4e63-9527-2b77f8fc0c78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_9f3f5301-22bc-4c26-9184-61d0a8857766" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_9fb531bb-0207-4e63-9527-2b77f8fc0c78" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_9f3f5301-22bc-4c26-9184-61d0a8857766" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_35dba29b-e652-4c47-a4fe-8de42befe847" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_9fb531bb-0207-4e63-9527-2b77f8fc0c78" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_35dba29b-e652-4c47-a4fe-8de42befe847" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_5928cf2e-b07f-4663-add4-3f8b60130da1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a0b86feb-a564-4fa0-adfb-805225c8114a" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_5928cf2e-b07f-4663-add4-3f8b60130da1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_f2ef0b7a-c8f1-4bdf-a44d-a50041aa2de4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a0b86feb-a564-4fa0-adfb-805225c8114a" xlink:to="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_f2ef0b7a-c8f1-4bdf-a44d-a50041aa2de4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths_f83629c1-8605-42ed-b6e3-91ed5e8c59f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_f2ef0b7a-c8f1-4bdf-a44d-a50041aa2de4" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths_f83629c1-8605-42ed-b6e3-91ed5e8c59f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo_7621c46d-a929-4ec3-817b-d177cd455630" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_f2ef0b7a-c8f1-4bdf-a44d-a50041aa2de4" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo_7621c46d-a929-4ec3-817b-d177cd455630" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree_862da336-e818-4b30-b9db-16fc2e857b3c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_f2ef0b7a-c8f1-4bdf-a44d-a50041aa2de4" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree_862da336-e818-4b30-b9db-16fc2e857b3c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour_0a000657-07c9-475b-afea-d705d4829440" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_f2ef0b7a-c8f1-4bdf-a44d-a50041aa2de4" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour_0a000657-07c9-475b-afea-d705d4829440" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive_f4a6747d-e362-4bd1-adae-b89b403bacc9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_f2ef0b7a-c8f1-4bdf-a44d-a50041aa2de4" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive_f4a6747d-e362-4bd1-adae-b89b403bacc9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter_9b02ebeb-4fcf-4a7b-ae3a-716b665e7980" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_f2ef0b7a-c8f1-4bdf-a44d-a50041aa2de4" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter_9b02ebeb-4fcf-4a7b-ae3a-716b665e7980" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/EquityPlansNarrativeDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#EquityPlansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/EquityPlansNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OptionIndexedToIssuersEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityEquityTable_d4eb7756-7420-4441-912c-977e54eec2a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OptionIndexedToIssuersEquityEquityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityEquityTable_d4eb7756-7420-4441-912c-977e54eec2a2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_baac08fd-ffac-4c11-99e8-c5a019829bfa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityEquityTable_d4eb7756-7420-4441-912c-977e54eec2a2" xlink:to="loc_us-gaap_PlanNameAxis_baac08fd-ffac-4c11-99e8-c5a019829bfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_baac08fd-ffac-4c11-99e8-c5a019829bfa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_baac08fd-ffac-4c11-99e8-c5a019829bfa" xlink:to="loc_us-gaap_PlanNameDomain_baac08fd-ffac-4c11-99e8-c5a019829bfa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_fd62c2f8-de19-44f4-a174-1506b990970f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_baac08fd-ffac-4c11-99e8-c5a019829bfa" xlink:to="loc_us-gaap_PlanNameDomain_fd62c2f8-de19-44f4-a174-1506b990970f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_IncentivePlanMember_77a36dbf-8655-45d4-845c-00a91917135b" xlink:href="hto-20251231.xsd#hto_IncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_fd62c2f8-de19-44f4-a174-1506b990970f" xlink:to="loc_hto_IncentivePlanMember_77a36dbf-8655-45d4-845c-00a91917135b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_EmployeeStockPurchasePlanMember_4a0a72d7-b889-4679-8baf-643f8331dc2f" xlink:href="hto-20251231.xsd#hto_EmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_fd62c2f8-de19-44f4-a174-1506b990970f" xlink:to="loc_hto_EmployeeStockPurchasePlanMember_4a0a72d7-b889-4679-8baf-643f8331dc2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_bf51a19e-79ae-4fdb-88a7-06e752c28766" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityEquityTable_d4eb7756-7420-4441-912c-977e54eec2a2" xlink:to="loc_us-gaap_StatementClassOfStockAxis_bf51a19e-79ae-4fdb-88a7-06e752c28766" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_bf51a19e-79ae-4fdb-88a7-06e752c28766_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_bf51a19e-79ae-4fdb-88a7-06e752c28766" xlink:to="loc_us-gaap_ClassOfStockDomain_bf51a19e-79ae-4fdb-88a7-06e752c28766_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_35983f01-5c40-4d0a-af91-a0a7382b1a93" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_bf51a19e-79ae-4fdb-88a7-06e752c28766" xlink:to="loc_us-gaap_ClassOfStockDomain_35983f01-5c40-4d0a-af91-a0a7382b1a93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_1fae5ea4-fed5-4501-98d5-1595c1f56b5e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_35983f01-5c40-4d0a-af91-a0a7382b1a93" xlink:to="loc_us-gaap_CommonStockMember_1fae5ea4-fed5-4501-98d5-1595c1f56b5e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_f62fd7f8-ce64-4b7f-a7e2-86c13399784a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityEquityTable_d4eb7756-7420-4441-912c-977e54eec2a2" xlink:to="loc_us-gaap_AwardTypeAxis_f62fd7f8-ce64-4b7f-a7e2-86c13399784a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f62fd7f8-ce64-4b7f-a7e2-86c13399784a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_f62fd7f8-ce64-4b7f-a7e2-86c13399784a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f62fd7f8-ce64-4b7f-a7e2-86c13399784a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6f5b6ac8-305d-4ccc-88ba-4eda7e63a07b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_f62fd7f8-ce64-4b7f-a7e2-86c13399784a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6f5b6ac8-305d-4ccc-88ba-4eda7e63a07b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RestrictedStockAndDeferredRestrictedStockMember_96f1ac0f-24d3-4073-8350-213b5900a072" xlink:href="hto-20251231.xsd#hto_RestrictedStockAndDeferredRestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6f5b6ac8-305d-4ccc-88ba-4eda7e63a07b" xlink:to="loc_hto_RestrictedStockAndDeferredRestrictedStockMember_96f1ac0f-24d3-4073-8350-213b5900a072" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_39babb15-b335-4012-b8ba-5735f29c81a9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6f5b6ac8-305d-4ccc-88ba-4eda7e63a07b" xlink:to="loc_us-gaap_PerformanceSharesMember_39babb15-b335-4012-b8ba-5735f29c81a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_MarketbasedRSUMember_01fecaa1-8e19-484c-9c67-56e4f842dd2a" xlink:href="hto-20251231.xsd#hto_MarketbasedRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6f5b6ac8-305d-4ccc-88ba-4eda7e63a07b" xlink:to="loc_hto_MarketbasedRSUMember_01fecaa1-8e19-484c-9c67-56e4f842dd2a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_de18dedb-6316-4943-b70c-ac94782c3a97" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityEquityTable_d4eb7756-7420-4441-912c-977e54eec2a2" xlink:to="loc_srt_RangeAxis_de18dedb-6316-4943-b70c-ac94782c3a97" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_de18dedb-6316-4943-b70c-ac94782c3a97_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_de18dedb-6316-4943-b70c-ac94782c3a97" xlink:to="loc_srt_RangeMember_de18dedb-6316-4943-b70c-ac94782c3a97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_6d8b566c-e640-43f7-a90f-0aab0b0c7f84" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_de18dedb-6316-4943-b70c-ac94782c3a97" xlink:to="loc_srt_RangeMember_6d8b566c-e640-43f7-a90f-0aab0b0c7f84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_1562b894-52c8-43ab-8180-f3a072b99b23" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_6d8b566c-e640-43f7-a90f-0aab0b0c7f84" xlink:to="loc_srt_MinimumMember_1562b894-52c8-43ab-8180-f3a072b99b23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_935c6ec6-bbbd-4c48-899f-560db3491f47" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_6d8b566c-e640-43f7-a90f-0aab0b0c7f84" xlink:to="loc_srt_MaximumMember_935c6ec6-bbbd-4c48-899f-560db3491f47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_48ff03c3-f60e-4d03-97bc-c7469150b5b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_48ff03c3-f60e-4d03-97bc-c7469150b5b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_0777703d-7b63-4806-8eef-e3f62e179665" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_0777703d-7b63-4806-8eef-e3f62e179665" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee_7abdc743-7c7f-4039-9144-1ae59127e6df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee_7abdc743-7c7f-4039-9144-1ae59127e6df" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedPursuantToPlan_0d6de7a9-1dea-406b-aa96-773b181ca270" xlink:href="hto-20251231.xsd#hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedPursuantToPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedPursuantToPlan_0d6de7a9-1dea-406b-aa96-773b181ca270" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuableUponVesting_b72b9b40-45d7-47f2-9a8d-f29e0b64d917" xlink:href="hto-20251231.xsd#hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuableUponVesting"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuableUponVesting_b72b9b40-45d7-47f2-9a8d-f29e0b64d917" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsVestedGrantDateFairValue_53dbaf1f-7619-466a-b0be-7da9b81d7d63" xlink:href="hto-20251231.xsd#hto_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsVestedGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_hto_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsVestedGrantDateFairValue_53dbaf1f-7619-466a-b0be-7da9b81d7d63" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_48ecb656-5310-49cd-956c-b2f6ea21b944" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_48ecb656-5310-49cd-956c-b2f6ea21b944" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_80a1fb04-229e-420b-8871-bcccc29bacb1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_80a1fb04-229e-420b-8871-bcccc29bacb1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RestrictedStockAwardsPerformancebasedIssuedIntrinsicValue_f785c573-be25-4012-87b4-bcce9c1e365b" xlink:href="hto-20251231.xsd#hto_RestrictedStockAwardsPerformancebasedIssuedIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_hto_RestrictedStockAwardsPerformancebasedIssuedIntrinsicValue_f785c573-be25-4012-87b4-bcce9c1e365b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_7256bbd4-f861-4211-bf9b-fda3ef35c1ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_7256bbd4-f861-4211-bf9b-fda3ef35c1ca" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RestrictedStockAwardsPerformancebasedVestedBalance_d5874205-dc95-400a-918f-1c57c5937665" xlink:href="hto-20251231.xsd#hto_RestrictedStockAwardsPerformancebasedVestedBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_hto_RestrictedStockAwardsPerformancebasedVestedBalance_d5874205-dc95-400a-918f-1c57c5937665" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RestrictedStockAwardsPerformancebasedOutstandingBalance_8c92ed7a-a327-4975-a433-5b2edcd6f332" xlink:href="hto-20251231.xsd#hto_RestrictedStockAwardsPerformancebasedOutstandingBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_hto_RestrictedStockAwardsPerformancebasedOutstandingBalance_8c92ed7a-a327-4975-a433-5b2edcd6f332" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_94a4225c-033c-4aa6-95dc-f101611e3e33" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_94a4225c-033c-4aa6-95dc-f101611e3e33" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_8073aa35-02d2-4a3e-8135-db28cb239fcc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_8073aa35-02d2-4a3e-8135-db28cb239fcc" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_14d58ddf-fc5d-4816-a724-4c28be7da9c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityLineItems_ef980dd6-682b-4cff-903b-1ea3dd35905f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_14d58ddf-fc5d-4816-a724-4c28be7da9c9" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/EquityPlansScheduleofCompensationCostforSharebasedPaymentArrangementsAllocationofSharebasedCompensationCostsbyPlanDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#EquityPlansScheduleofCompensationCostforSharebasedPaymentArrangementsAllocationofSharebasedCompensationCostsbyPlanDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/EquityPlansScheduleofCompensationCostforSharebasedPaymentArrangementsAllocationofSharebasedCompensationCostsbyPlanDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_37145c00-0e2a-4860-85db-b71a2fac7161" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_78098e41-02a3-4a50-92b4-a3b757a4bbf0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_37145c00-0e2a-4860-85db-b71a2fac7161" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_78098e41-02a3-4a50-92b4-a3b757a4bbf0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_88d1ae9b-1009-4166-9ba0-8a592d1f078b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_78098e41-02a3-4a50-92b4-a3b757a4bbf0" xlink:to="loc_us-gaap_PlanNameAxis_88d1ae9b-1009-4166-9ba0-8a592d1f078b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_88d1ae9b-1009-4166-9ba0-8a592d1f078b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_88d1ae9b-1009-4166-9ba0-8a592d1f078b" xlink:to="loc_us-gaap_PlanNameDomain_88d1ae9b-1009-4166-9ba0-8a592d1f078b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_3ad71c24-c363-497f-bc6b-b962afbd3f37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_88d1ae9b-1009-4166-9ba0-8a592d1f078b" xlink:to="loc_us-gaap_PlanNameDomain_3ad71c24-c363-497f-bc6b-b962afbd3f37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_EmployeeStockPurchasePlanMember_5ab8079a-37fd-468e-b13a-e25fb2aacef8" xlink:href="hto-20251231.xsd#hto_EmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_3ad71c24-c363-497f-bc6b-b962afbd3f37" xlink:to="loc_hto_EmployeeStockPurchasePlanMember_5ab8079a-37fd-468e-b13a-e25fb2aacef8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_80a43e28-86fe-4dd8-9eb5-23719e62cc25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_78098e41-02a3-4a50-92b4-a3b757a4bbf0" xlink:to="loc_us-gaap_AwardTypeAxis_80a43e28-86fe-4dd8-9eb5-23719e62cc25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_80a43e28-86fe-4dd8-9eb5-23719e62cc25_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_80a43e28-86fe-4dd8-9eb5-23719e62cc25" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_80a43e28-86fe-4dd8-9eb5-23719e62cc25_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_99f880d6-c11f-4441-94f0-b38c8e8f64ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_80a43e28-86fe-4dd8-9eb5-23719e62cc25" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_99f880d6-c11f-4441-94f0-b38c8e8f64ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RestrictedStockAndDeferredRestrictedStockMember_2cc03060-3a93-44bd-83b5-d7f81fcb7ff1" xlink:href="hto-20251231.xsd#hto_RestrictedStockAndDeferredRestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_99f880d6-c11f-4441-94f0-b38c8e8f64ad" xlink:to="loc_hto_RestrictedStockAndDeferredRestrictedStockMember_2cc03060-3a93-44bd-83b5-d7f81fcb7ff1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_c8726ec0-abae-47d1-88bf-d63ecb023557" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_37145c00-0e2a-4860-85db-b71a2fac7161" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_c8726ec0-abae-47d1-88bf-d63ecb023557" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_1fe5520f-f014-48cd-8fc5-00e9ea7c1964" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_37145c00-0e2a-4860-85db-b71a2fac7161" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_1fe5520f-f014-48cd-8fc5-00e9ea7c1964" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/EquityPlansScheduleofRestrictedStockandDeferredRestrictedStockActivityDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#EquityPlansScheduleofRestrictedStockandDeferredRestrictedStockActivityDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/EquityPlansScheduleofRestrictedStockandDeferredRestrictedStockActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43b82d8a-8572-4062-9bb3-1b19e0c87e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0b813b1c-8ea7-48da-9de0-4b8892397fa4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43b82d8a-8572-4062-9bb3-1b19e0c87e5d" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0b813b1c-8ea7-48da-9de0-4b8892397fa4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_55761068-e38e-4fbb-a634-ebd07d9937f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0b813b1c-8ea7-48da-9de0-4b8892397fa4" xlink:to="loc_us-gaap_AwardTypeAxis_55761068-e38e-4fbb-a634-ebd07d9937f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_55761068-e38e-4fbb-a634-ebd07d9937f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_55761068-e38e-4fbb-a634-ebd07d9937f2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_55761068-e38e-4fbb-a634-ebd07d9937f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cd028a15-5dc6-49dd-9c12-e638ebab5176" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_55761068-e38e-4fbb-a634-ebd07d9937f2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cd028a15-5dc6-49dd-9c12-e638ebab5176" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_RestrictedStockAndDeferredRestrictedStockMember_c7f24f32-1db7-4718-9d6c-cf9ff690cae1" xlink:href="hto-20251231.xsd#hto_RestrictedStockAndDeferredRestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cd028a15-5dc6-49dd-9c12-e638ebab5176" xlink:to="loc_hto_RestrictedStockAndDeferredRestrictedStockMember_c7f24f32-1db7-4718-9d6c-cf9ff690cae1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_8f98eabd-996f-4cd8-91e7-72236f2440f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0b813b1c-8ea7-48da-9de0-4b8892397fa4" xlink:to="loc_us-gaap_PlanNameAxis_8f98eabd-996f-4cd8-91e7-72236f2440f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_8f98eabd-996f-4cd8-91e7-72236f2440f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_8f98eabd-996f-4cd8-91e7-72236f2440f4" xlink:to="loc_us-gaap_PlanNameDomain_8f98eabd-996f-4cd8-91e7-72236f2440f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_14ff4a53-9637-4464-9318-7cdfd80488a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_8f98eabd-996f-4cd8-91e7-72236f2440f4" xlink:to="loc_us-gaap_PlanNameDomain_14ff4a53-9637-4464-9318-7cdfd80488a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_IncentivePlanMember_34fd1e90-ab7f-4889-9834-144606709ac3" xlink:href="hto-20251231.xsd#hto_IncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_14ff4a53-9637-4464-9318-7cdfd80488a6" xlink:to="loc_hto_IncentivePlanMember_34fd1e90-ab7f-4889-9834-144606709ac3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_3f58565d-6aee-41f1-9709-f3a0549c3307" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43b82d8a-8572-4062-9bb3-1b19e0c87e5d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_3f58565d-6aee-41f1-9709-f3a0549c3307" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_69125955-c40c-435f-9c0a-9706ed3bd000" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_3f58565d-6aee-41f1-9709-f3a0549c3307" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_69125955-c40c-435f-9c0a-9706ed3bd000" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_bec1e01a-fa87-4bca-a2e1-7c6ed523fd81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_3f58565d-6aee-41f1-9709-f3a0549c3307" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_bec1e01a-fa87-4bca-a2e1-7c6ed523fd81" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_820f4f06-2e8c-4221-a618-920e5b483b17" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_3f58565d-6aee-41f1-9709-f3a0549c3307" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_820f4f06-2e8c-4221-a618-920e5b483b17" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations_c174bb29-fc65-49c0-b52b-3948aa5344fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_3f58565d-6aee-41f1-9709-f3a0549c3307" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations_c174bb29-fc65-49c0-b52b-3948aa5344fd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_6c068dbf-d49d-40d6-9fb9-b0c2fc61f577" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedNumber_221ab2cb-acad-422c-8af4-6ab2d9321c4f" xlink:href="hto-20251231.xsd#hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43b82d8a-8572-4062-9bb3-1b19e0c87e5d" xlink:to="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedNumber_221ab2cb-acad-422c-8af4-6ab2d9321c4f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsWeightedAverageGrantDateFairValueRollForwardRollForward_e20ddaa8-a850-4e6c-a077-ba802fdc0dcb" xlink:href="hto-20251231.xsd#hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsWeightedAverageGrantDateFairValueRollForwardRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43b82d8a-8572-4062-9bb3-1b19e0c87e5d" xlink:to="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsWeightedAverageGrantDateFairValueRollForwardRollForward_e20ddaa8-a850-4e6c-a077-ba802fdc0dcb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue_161bca39-a5d4-4f00-9115-efc2388c866e" xlink:href="hto-20251231.xsd#hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsWeightedAverageGrantDateFairValueRollForwardRollForward_e20ddaa8-a850-4e6c-a077-ba802fdc0dcb" xlink:to="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue_161bca39-a5d4-4f00-9115-efc2388c866e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedWeightedAverageGrantDateFairValue_547d8d01-9d52-46e3-b9d3-c343a1798769" xlink:href="hto-20251231.xsd#hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsWeightedAverageGrantDateFairValueRollForwardRollForward_e20ddaa8-a850-4e6c-a077-ba802fdc0dcb" xlink:to="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedWeightedAverageGrantDateFairValue_547d8d01-9d52-46e3-b9d3-c343a1798769" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisedWeightedAverageGrantDateFairValue_8397a458-634b-4083-8edd-1c96d6fb16e6" xlink:href="hto-20251231.xsd#hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsWeightedAverageGrantDateFairValueRollForwardRollForward_e20ddaa8-a850-4e6c-a077-ba802fdc0dcb" xlink:to="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisedWeightedAverageGrantDateFairValue_8397a458-634b-4083-8edd-1c96d6fb16e6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirationsWeightedAverageGrantDateFairValue_1f1eac5b-37a9-49c9-bb4d-900d36ca8d6f" xlink:href="hto-20251231.xsd#hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirationsWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsWeightedAverageGrantDateFairValueRollForwardRollForward_e20ddaa8-a850-4e6c-a077-ba802fdc0dcb" xlink:to="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirationsWeightedAverageGrantDateFairValue_1f1eac5b-37a9-49c9-bb4d-900d36ca8d6f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue_4dcdb9c1-8592-4f43-b94b-27489f54c5c2" xlink:href="hto-20251231.xsd#hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedWeightedAverageGrantDateFairValue_6b181020-4acd-47e8-8f94-f0410155cfd9" xlink:href="hto-20251231.xsd#hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43b82d8a-8572-4062-9bb3-1b19e0c87e5d" xlink:to="loc_hto_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedWeightedAverageGrantDateFairValue_6b181020-4acd-47e8-8f94-f0410155cfd9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ea66b993-5bfd-41c1-9f50-5db2882f23c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43b82d8a-8572-4062-9bb3-1b19e0c87e5d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ea66b993-5bfd-41c1-9f50-5db2882f23c5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_cb89edf7-cd98-4714-ba44-06a43b415934" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ea66b993-5bfd-41c1-9f50-5db2882f23c5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_cb89edf7-cd98-4714-ba44-06a43b415934" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_df46817f-85bf-402c-afa2-015e21f6251d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ea66b993-5bfd-41c1-9f50-5db2882f23c5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_df46817f-85bf-402c-afa2-015e21f6251d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_45bdf67e-33c9-444f-9cfd-03e55222d738" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ea66b993-5bfd-41c1-9f50-5db2882f23c5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_45bdf67e-33c9-444f-9cfd-03e55222d738" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_e931a2f9-bd57-464d-937b-a4d91c4262d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ea66b993-5bfd-41c1-9f50-5db2882f23c5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_e931a2f9-bd57-464d-937b-a4d91c4262d3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_032a0b02-073e-486d-9a3c-24bfc6a05002" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_2dda5986-6dae-41b7-8a1a-1a7ebe294f6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43b82d8a-8572-4062-9bb3-1b19e0c87e5d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_2dda5986-6dae-41b7-8a1a-1a7ebe294f6d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_d8df3ab5-03ff-4bd3-9fce-76b0c26bbb09" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_2dda5986-6dae-41b7-8a1a-1a7ebe294f6d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_d8df3ab5-03ff-4bd3-9fce-76b0c26bbb09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_8d9a20db-38af-456d-be46-ee694fc4542a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_2dda5986-6dae-41b7-8a1a-1a7ebe294f6d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_8d9a20db-38af-456d-be46-ee694fc4542a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_69bad521-7ef1-459f-853a-0308606d8c80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_2dda5986-6dae-41b7-8a1a-1a7ebe294f6d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_69bad521-7ef1-459f-853a-0308606d8c80" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_7d0b5488-706f-4c6d-b949-eb3de0be5ae8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_2dda5986-6dae-41b7-8a1a-1a7ebe294f6d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_7d0b5488-706f-4c6d-b949-eb3de0be5ae8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_31b0b680-4673-4070-b6ce-cd909a9c254c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/SegmentReportingReportableSegmentInformationDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#SegmentReportingReportableSegmentInformationDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/SegmentReportingReportableSegmentInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_35b869f3-283a-4cb3-b250-0de055d9b819" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_4d4b4652-d4eb-4ba6-977a-026674cc474b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_35b869f3-283a-4cb3-b250-0de055d9b819" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_4d4b4652-d4eb-4ba6-977a-026674cc474b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_fa0cce31-907d-4d73-b90b-853aeae44fae" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_4d4b4652-d4eb-4ba6-977a-026674cc474b" xlink:to="loc_srt_ConsolidationItemsAxis_fa0cce31-907d-4d73-b90b-853aeae44fae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_fa0cce31-907d-4d73-b90b-853aeae44fae_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_fa0cce31-907d-4d73-b90b-853aeae44fae" xlink:to="loc_srt_ConsolidationItemsDomain_fa0cce31-907d-4d73-b90b-853aeae44fae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_e3ddd784-28a8-4239-94f6-57aa8255b911" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_fa0cce31-907d-4d73-b90b-853aeae44fae" xlink:to="loc_srt_ConsolidationItemsDomain_e3ddd784-28a8-4239-94f6-57aa8255b911" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_a1c92a4c-edf4-4915-aeb6-d80158b0d383" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_e3ddd784-28a8-4239-94f6-57aa8255b911" xlink:to="loc_us-gaap_OperatingSegmentsMember_a1c92a4c-edf4-4915-aeb6-d80158b0d383" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_bbd394e1-9e50-4f7b-ba8f-168e7cfee7f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MaterialReconcilingItemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_e3ddd784-28a8-4239-94f6-57aa8255b911" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_bbd394e1-9e50-4f7b-ba8f-168e7cfee7f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_559c8de5-6bf1-48ee-9ff9-5ff88548bd9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_e3ddd784-28a8-4239-94f6-57aa8255b911" xlink:to="loc_us-gaap_CorporateNonSegmentMember_559c8de5-6bf1-48ee-9ff9-5ff88548bd9a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_2c07bfec-57da-451b-8f0f-f4ab30165649" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_4d4b4652-d4eb-4ba6-977a-026674cc474b" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_2c07bfec-57da-451b-8f0f-f4ab30165649" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_2c07bfec-57da-451b-8f0f-f4ab30165649_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_2c07bfec-57da-451b-8f0f-f4ab30165649" xlink:to="loc_us-gaap_SegmentDomain_2c07bfec-57da-451b-8f0f-f4ab30165649_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_7582eb7b-023c-4c82-84fb-2b3b0d95cc0c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_2c07bfec-57da-451b-8f0f-f4ab30165649" xlink:to="loc_us-gaap_SegmentDomain_7582eb7b-023c-4c82-84fb-2b3b0d95cc0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_WaterUtilityServicesMember_5848c038-e663-46ac-ad80-9f917fb8d272" xlink:href="hto-20251231.xsd#hto_WaterUtilityServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_7582eb7b-023c-4c82-84fb-2b3b0d95cc0c" xlink:to="loc_hto_WaterUtilityServicesMember_5848c038-e663-46ac-ad80-9f917fb8d272" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_9924036b-dc3f-4713-9d2c-0a065dec24a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_35b869f3-283a-4cb3-b250-0de055d9b819" xlink:to="loc_us-gaap_Revenues_9924036b-dc3f-4713-9d2c-0a065dec24a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_5e2913ab-80c7-40aa-841d-8b5f0dbe3f43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_35b869f3-283a-4cb3-b250-0de055d9b819" xlink:to="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_5e2913ab-80c7-40aa-841d-8b5f0dbe3f43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WaterProductionCosts_bd727425-2bbc-4fc1-958d-49e93088f3d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WaterProductionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_5e2913ab-80c7-40aa-841d-8b5f0dbe3f43" xlink:to="loc_us-gaap_WaterProductionCosts_bd727425-2bbc-4fc1-958d-49e93088f3d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_e8e627f9-38f4-4c34-97d3-cbfa468009d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_5e2913ab-80c7-40aa-841d-8b5f0dbe3f43" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_e8e627f9-38f4-4c34-97d3-cbfa468009d2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenance_f0607109-22a4-438c-b378-115caa426085" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UtilitiesOperatingExpenseMaintenance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_5e2913ab-80c7-40aa-841d-8b5f0dbe3f43" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenance_f0607109-22a4-438c-b378-115caa426085" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseTaxes_eb69374b-8626-4825-a75a-35f39787b5d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UtilitiesOperatingExpenseTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_5e2913ab-80c7-40aa-841d-8b5f0dbe3f43" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseTaxes_eb69374b-8626-4825-a75a-35f39787b5d4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization_a7d03b0a-4b9b-4023-91fe-ba0d4bcbbc31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_5e2913ab-80c7-40aa-841d-8b5f0dbe3f43" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization_a7d03b0a-4b9b-4023-91fe-ba0d4bcbbc31" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_702adaa0-337a-4101-99ed-8981c5a1c4b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_5e2913ab-80c7-40aa-841d-8b5f0dbe3f43" xlink:to="loc_us-gaap_InterestExpenseDebt_702adaa0-337a-4101-99ed-8981c5a1c4b0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_3ea51a05-b119-4aea-9bd3-1710bd3177bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_5e2913ab-80c7-40aa-841d-8b5f0dbe3f43" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_3ea51a05-b119-4aea-9bd3-1710bd3177bb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_cfa50464-6caf-46b7-afb8-5bd2ce87af1c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_5e2913ab-80c7-40aa-841d-8b5f0dbe3f43" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_cfa50464-6caf-46b7-afb8-5bd2ce87af1c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_cb3e1b3b-306b-4b51-ad76-8754caa88a95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_35b869f3-283a-4cb3-b250-0de055d9b819" xlink:to="loc_us-gaap_NetIncomeLoss_cb3e1b3b-306b-4b51-ad76-8754caa88a95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_a8201a0f-f731-49a6-bdb8-9c574a804939" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_35b869f3-283a-4cb3-b250-0de055d9b819" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_a8201a0f-f731-49a6-bdb8-9c574a804939" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_c6170433-1d30-439e-86a5-c15629c515fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_35b869f3-283a-4cb3-b250-0de055d9b819" xlink:to="loc_us-gaap_Assets_c6170433-1d30-439e-86a5-c15629c515fb" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/AcquisitionsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#AcquisitionsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/AcquisitionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019b6948-0cf6-7700-a74a-a30be279f527" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_efe2bf74-12b7-46f8-a185-d93d7f3604a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019b6948-0cf6-7700-a74a-a30be279f527" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_efe2bf74-12b7-46f8-a185-d93d7f3604a4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionAxis_019b6948-0cf6-710f-99cc-805b65bdae59" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_efe2bf74-12b7-46f8-a185-d93d7f3604a4" xlink:to="loc_us-gaap_AssetAcquisitionAxis_019b6948-0cf6-710f-99cc-805b65bdae59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019b6948-0cf6-710f-99cc-805b65bdae59_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetAcquisitionAxis_019b6948-0cf6-710f-99cc-805b65bdae59" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019b6948-0cf6-710f-99cc-805b65bdae59_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019b6948-0cf6-7b2a-b2ad-cbb90424b5d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetAcquisitionAxis_019b6948-0cf6-710f-99cc-805b65bdae59" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019b6948-0cf6-7b2a-b2ad-cbb90424b5d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_QuadvestRetailAssetPurchaseAgreementMember_019b6948-0cf6-7a14-a9d7-ec542f216644" xlink:href="hto-20251231.xsd#hto_QuadvestRetailAssetPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_019b6948-0cf6-7b2a-b2ad-cbb90424b5d4" xlink:to="loc_hto_QuadvestRetailAssetPurchaseAgreementMember_019b6948-0cf6-7a14-a9d7-ec542f216644" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_QuadvestWholesaleAssetPurchaseAgreementMember_019b6948-0cf6-703b-992f-fc06a14da744" xlink:href="hto-20251231.xsd#hto_QuadvestWholesaleAssetPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_019b6948-0cf6-7b2a-b2ad-cbb90424b5d4" xlink:to="loc_hto_QuadvestWholesaleAssetPurchaseAgreementMember_019b6948-0cf6-703b-992f-fc06a14da744" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionConsiderationTransferred_019b6948-0cf6-7023-a3b7-bcd2ac762077" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019b6948-0cf6-7700-a74a-a30be279f527" xlink:to="loc_us-gaap_AssetAcquisitionConsiderationTransferred_019b6948-0cf6-7023-a3b7-bcd2ac762077" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_AssetAcquisitionNumberOfAppraisers_019c77f6-aa72-7d3f-a810-5dc3f85a123b" xlink:href="hto-20251231.xsd#hto_AssetAcquisitionNumberOfAppraisers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019b6948-0cf6-7700-a74a-a30be279f527" xlink:to="loc_hto_AssetAcquisitionNumberOfAppraisers_019c77f6-aa72-7d3f-a810-5dc3f85a123b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/FINANCIALSTATEMENTSCHEDULECondensedBalanceSheetsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#FINANCIALSTATEMENTSCHEDULECondensedBalanceSheetsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/FINANCIALSTATEMENTSCHEDULECondensedBalanceSheetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedFinancialStatementsCaptionsLineItems_53cdb4d6-be11-4963-8547-16910564e64d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CondensedFinancialStatementsCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedFinancialStatementsTable_53df6f20-0a4e-48e3-9468-45f04f880f3c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfCondensedFinancialStatementsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_53cdb4d6-be11-4963-8547-16910564e64d" xlink:to="loc_srt_ScheduleOfCondensedFinancialStatementsTable_53df6f20-0a4e-48e3-9468-45f04f880f3c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_583b34a8-7440-43c5-91ca-30ae7857dbf1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_53df6f20-0a4e-48e3-9468-45f04f880f3c" xlink:to="loc_srt_ConsolidatedEntitiesAxis_583b34a8-7440-43c5-91ca-30ae7857dbf1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_583b34a8-7440-43c5-91ca-30ae7857dbf1_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_583b34a8-7440-43c5-91ca-30ae7857dbf1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_583b34a8-7440-43c5-91ca-30ae7857dbf1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_d334d1f7-59f6-4ea8-b6dc-fde9e7c678e1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_583b34a8-7440-43c5-91ca-30ae7857dbf1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_d334d1f7-59f6-4ea8-b6dc-fde9e7c678e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ParentCompanyMember_a65ec623-45fb-4a6b-8484-e28a886172b1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ParentCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_d334d1f7-59f6-4ea8-b6dc-fde9e7c678e1" xlink:to="loc_srt_ParentCompanyMember_a65ec623-45fb-4a6b-8484-e28a886172b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_dfc0c5a2-01e1-4858-9147-f3a0dcc8f6fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_53cdb4d6-be11-4963-8547-16910564e64d" xlink:to="loc_us-gaap_AssetsAbstract_dfc0c5a2-01e1-4858-9147-f3a0dcc8f6fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_InvestmentsInSubsidiaries_41aeb36b-bdeb-4603-8d87-8f42b75471e3" xlink:href="hto-20251231.xsd#hto_InvestmentsInSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_dfc0c5a2-01e1-4858-9147-f3a0dcc8f6fc" xlink:to="loc_hto_InvestmentsInSubsidiaries_41aeb36b-bdeb-4603-8d87-8f42b75471e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_2e314e41-4557-4461-b6f4-f2cb78d4c6e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_dfc0c5a2-01e1-4858-9147-f3a0dcc8f6fc" xlink:to="loc_us-gaap_AssetsCurrentAbstract_2e314e41-4557-4461-b6f4-f2cb78d4c6e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_76fb272c-2439-4ab6-9f50-808a2e195667" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_2e314e41-4557-4461-b6f4-f2cb78d4c6e5" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_76fb272c-2439-4ab6-9f50-808a2e195667" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_IntercompanyReceivablesCurrent_ed569bd2-2549-4fd5-87a7-3d6b334077c1" xlink:href="hto-20251231.xsd#hto_IntercompanyReceivablesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_2e314e41-4557-4461-b6f4-f2cb78d4c6e5" xlink:to="loc_hto_IntercompanyReceivablesCurrent_ed569bd2-2549-4fd5-87a7-3d6b334077c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_IntercompanyNotesReceivableCurrent_b2b96467-1a6e-40e6-81d9-da0756075702" xlink:href="hto-20251231.xsd#hto_IntercompanyNotesReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_2e314e41-4557-4461-b6f4-f2cb78d4c6e5" xlink:to="loc_hto_IntercompanyNotesReceivableCurrent_b2b96467-1a6e-40e6-81d9-da0756075702" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_5c272750-1a41-469e-8798-c516e3d04394" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_2e314e41-4557-4461-b6f4-f2cb78d4c6e5" xlink:to="loc_us-gaap_OtherAssetsCurrent_5c272750-1a41-469e-8798-c516e3d04394" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_7f81154d-da0c-4658-87c3-3501a68b7e85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_2e314e41-4557-4461-b6f4-f2cb78d4c6e5" xlink:to="loc_us-gaap_AssetsCurrent_7f81154d-da0c-4658-87c3-3501a68b7e85" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrentAbstract_2c142189-d7ad-43b4-b789-96e7cb57c964" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_dfc0c5a2-01e1-4858-9147-f3a0dcc8f6fc" xlink:to="loc_us-gaap_OtherAssetsNoncurrentAbstract_2c142189-d7ad-43b4-b789-96e7cb57c964" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsMiscellaneousNoncurrent_fe125923-5d5a-4e21-b74b-96e981099c64" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsMiscellaneousNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherAssetsNoncurrentAbstract_2c142189-d7ad-43b4-b789-96e7cb57c964" xlink:to="loc_us-gaap_OtherAssetsMiscellaneousNoncurrent_fe125923-5d5a-4e21-b74b-96e981099c64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_6cd67155-d957-4954-b72d-3efffe7a58bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherAssetsNoncurrentAbstract_2c142189-d7ad-43b4-b789-96e7cb57c964" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_6cd67155-d957-4954-b72d-3efffe7a58bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_02fd83d9-e761-4870-b265-d4975bbe9b9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_dfc0c5a2-01e1-4858-9147-f3a0dcc8f6fc" xlink:to="loc_us-gaap_Assets_02fd83d9-e761-4870-b265-d4975bbe9b9e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_90183e91-a0f6-4c09-89fd-26bab0a989c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_53cdb4d6-be11-4963-8547-16910564e64d" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_90183e91-a0f6-4c09-89fd-26bab0a989c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_6e868464-2255-4d13-97e9-56f65fe2f412" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizationLongtermDebtAndEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_90183e91-a0f6-4c09-89fd-26bab0a989c4" xlink:to="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_6e868464-2255-4d13-97e9-56f65fe2f412" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityNumberOfSharesParValueAndOtherDisclosuresAbstract_97a0e148-b002-4a41-ae8e-cab96e6299f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityNumberOfSharesParValueAndOtherDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_6e868464-2255-4d13-97e9-56f65fe2f412" xlink:to="loc_us-gaap_StockholdersEquityNumberOfSharesParValueAndOtherDisclosuresAbstract_97a0e148-b002-4a41-ae8e-cab96e6299f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_db729860-9ab5-467d-8f8f-2b4d5cc84e71" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityNumberOfSharesParValueAndOtherDisclosuresAbstract_97a0e148-b002-4a41-ae8e-cab96e6299f9" xlink:to="loc_us-gaap_CommonStockValue_db729860-9ab5-467d-8f8f-2b4d5cc84e71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_9fe9fe4a-bcf3-45bd-b871-0be15b185cf8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityNumberOfSharesParValueAndOtherDisclosuresAbstract_97a0e148-b002-4a41-ae8e-cab96e6299f9" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_9fe9fe4a-bcf3-45bd-b871-0be15b185cf8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_3dd8cfa4-2bfb-4ca8-a884-9138b8b3b52e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityNumberOfSharesParValueAndOtherDisclosuresAbstract_97a0e148-b002-4a41-ae8e-cab96e6299f9" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_3dd8cfa4-2bfb-4ca8-a884-9138b8b3b52e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_90354b65-f127-4fd3-a216-6731ab06444a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityNumberOfSharesParValueAndOtherDisclosuresAbstract_97a0e148-b002-4a41-ae8e-cab96e6299f9" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_90354b65-f127-4fd3-a216-6731ab06444a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_77e0b3bd-a3c1-4aea-8433-99110137ca57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityNumberOfSharesParValueAndOtherDisclosuresAbstract_97a0e148-b002-4a41-ae8e-cab96e6299f9" xlink:to="loc_us-gaap_StockholdersEquity_77e0b3bd-a3c1-4aea-8433-99110137ca57" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_d79213be-ea8e-43b7-85a6-4282c4dab134" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_6e868464-2255-4d13-97e9-56f65fe2f412" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_d79213be-ea8e-43b7-85a6-4282c4dab134" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizationLongtermDebtAndEquity_a5784460-a2af-4d5b-9dc5-7009cc0873b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizationLongtermDebtAndEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_6e868464-2255-4d13-97e9-56f65fe2f412" xlink:to="loc_us-gaap_CapitalizationLongtermDebtAndEquity_a5784460-a2af-4d5b-9dc5-7009cc0873b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_2e44b6bf-e684-48dc-af1d-36f9f3600c42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_90183e91-a0f6-4c09-89fd-26bab0a989c4" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_2e44b6bf-e684-48dc-af1d-36f9f3600c42" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LinesOfCreditCurrent_deb7d6b8-62e8-4d85-a708-9bb3d752cf42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LinesOfCreditCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2e44b6bf-e684-48dc-af1d-36f9f3600c42" xlink:to="loc_us-gaap_LinesOfCreditCurrent_deb7d6b8-62e8-4d85-a708-9bb3d752cf42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_IntercompanyPayableCurrent_c4d4dd3c-a7a2-4457-9312-9280cec3cc60" xlink:href="hto-20251231.xsd#hto_IntercompanyPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2e44b6bf-e684-48dc-af1d-36f9f3600c42" xlink:to="loc_hto_IntercompanyPayableCurrent_c4d4dd3c-a7a2-4457-9312-9280cec3cc60" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_IntercompanyNotesPayableCurrent_cd3bcfcd-bdfa-4cb6-ae3d-6ce7769fe549" xlink:href="hto-20251231.xsd#hto_IntercompanyNotesPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2e44b6bf-e684-48dc-af1d-36f9f3600c42" xlink:to="loc_hto_IntercompanyNotesPayableCurrent_cd3bcfcd-bdfa-4cb6-ae3d-6ce7769fe549" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_d5d2e1fb-c9c3-4dda-84bd-847191c33e09" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2e44b6bf-e684-48dc-af1d-36f9f3600c42" xlink:to="loc_us-gaap_AccountsPayableCurrent_d5d2e1fb-c9c3-4dda-84bd-847191c33e09" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_46b430ee-fecc-446f-bc40-9c6da409c385" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2e44b6bf-e684-48dc-af1d-36f9f3600c42" xlink:to="loc_us-gaap_InterestPayableCurrent_46b430ee-fecc-446f-bc40-9c6da409c385" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_IncomeTaxPayableCurrent_5b89d0f9-6df5-466a-b7b6-81fbf4182b61" xlink:href="hto-20251231.xsd#hto_IncomeTaxPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2e44b6bf-e684-48dc-af1d-36f9f3600c42" xlink:to="loc_hto_IncomeTaxPayableCurrent_5b89d0f9-6df5-466a-b7b6-81fbf4182b61" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_c2a2390f-16de-4a5d-ba37-079138cf36af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2e44b6bf-e684-48dc-af1d-36f9f3600c42" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_c2a2390f-16de-4a5d-ba37-079138cf36af" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_d6363435-c558-4d33-879a-2b35d4ef9f69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2e44b6bf-e684-48dc-af1d-36f9f3600c42" xlink:to="loc_us-gaap_LiabilitiesCurrent_d6363435-c558-4d33-879a-2b35d4ef9f69" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_61f12b67-9f3a-4bfb-bf22-9c7fdefeeab6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_90183e91-a0f6-4c09-89fd-26bab0a989c4" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_61f12b67-9f3a-4bfb-bf22-9c7fdefeeab6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_03569db2-9832-4ea5-ac20-570996f23028" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_90183e91-a0f6-4c09-89fd-26bab0a989c4" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_03569db2-9832-4ea5-ac20-570996f23028" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_ec95d528-4649-4553-bdfd-87c844e01973" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_90183e91-a0f6-4c09-89fd-26bab0a989c4" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_ec95d528-4649-4553-bdfd-87c844e01973" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_6be266ff-56b0-40a3-8d90-6eb63a6bd872" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_90183e91-a0f6-4c09-89fd-26bab0a989c4" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_6be266ff-56b0-40a3-8d90-6eb63a6bd872" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_52c9bc09-221e-42f5-aaf3-c311421543ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_90183e91-a0f6-4c09-89fd-26bab0a989c4" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_52c9bc09-221e-42f5-aaf3-c311421543ad" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_e018c27c-9e01-4b1b-bfe8-96a49b7606f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_90183e91-a0f6-4c09-89fd-26bab0a989c4" xlink:to="loc_us-gaap_CommonStockSharesIssued_e018c27c-9e01-4b1b-bfe8-96a49b7606f5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_48df7df9-5318-4016-b130-8e467b1b8ae0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_90183e91-a0f6-4c09-89fd-26bab0a989c4" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_48df7df9-5318-4016-b130-8e467b1b8ae0" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/FINANCIALSTATEMENTSCHEDULECondensedStatementsofComprehensiveIncomeDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#FINANCIALSTATEMENTSCHEDULECondensedStatementsofComprehensiveIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/FINANCIALSTATEMENTSCHEDULECondensedStatementsofComprehensiveIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CondensedFinancialStatementsCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedFinancialStatementsTable_26a8f3dd-abc7-4aac-b4b6-08e5343aab89" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfCondensedFinancialStatementsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:to="loc_srt_ScheduleOfCondensedFinancialStatementsTable_26a8f3dd-abc7-4aac-b4b6-08e5343aab89" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_6f1cfd1f-1e40-4b07-b81f-808edcb81817" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_26a8f3dd-abc7-4aac-b4b6-08e5343aab89" xlink:to="loc_srt_ConsolidatedEntitiesAxis_6f1cfd1f-1e40-4b07-b81f-808edcb81817" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_6f1cfd1f-1e40-4b07-b81f-808edcb81817_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_6f1cfd1f-1e40-4b07-b81f-808edcb81817" xlink:to="loc_srt_ConsolidatedEntitiesDomain_6f1cfd1f-1e40-4b07-b81f-808edcb81817_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_baed019e-e894-4506-a4d2-65fbb6181544" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_6f1cfd1f-1e40-4b07-b81f-808edcb81817" xlink:to="loc_srt_ConsolidatedEntitiesDomain_baed019e-e894-4506-a4d2-65fbb6181544" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ParentCompanyMember_d2570584-e724-4d5e-a35c-44c792cbc4de" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ParentCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_baed019e-e894-4506-a4d2-65fbb6181544" xlink:to="loc_srt_ParentCompanyMember_d2570584-e724-4d5e-a35c-44c792cbc4de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_e4ca73cc-a697-4c75-bea0-affa89a4b7fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:to="loc_us-gaap_Revenues_e4ca73cc-a697-4c75-bea0-affa89a4b7fa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_0ab0078f-bf7d-4757-b7a0-3efeda83114d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_0ab0078f-bf7d-4757-b7a0-3efeda83114d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_319feeba-1af1-4808-a73d-1b19fb3f121d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_0ab0078f-bf7d-4757-b7a0-3efeda83114d" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_319feeba-1af1-4808-a73d-1b19fb3f121d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseTaxes_32064b57-9b06-4fe0-905c-95e202198d60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UtilitiesOperatingExpenseTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_0ab0078f-bf7d-4757-b7a0-3efeda83114d" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseTaxes_32064b57-9b06-4fe0-905c-95e202198d60" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpense_f5cd330a-e4b8-4d44-90bb-db49ad6e261c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UtilitiesOperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_0ab0078f-bf7d-4757-b7a0-3efeda83114d" xlink:to="loc_us-gaap_UtilitiesOperatingExpense_f5cd330a-e4b8-4d44-90bb-db49ad6e261c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_dd458514-d608-4374-8d0f-e1240e29e683" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:to="loc_us-gaap_OperatingIncomeLoss_dd458514-d608-4374-8d0f-e1240e29e683" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_f5419d1b-8806-4af7-9701-a7965f01bd3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_f5419d1b-8806-4af7-9701-a7965f01bd3d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_2c98c7f3-e65a-48aa-aab6-dd6261953c61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_f5419d1b-8806-4af7-9701-a7965f01bd3d" xlink:to="loc_us-gaap_InterestExpenseDebt_2c98c7f3-e65a-48aa-aab6-dd6261953c61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_InterestIncomeOnIntercompanyNotesReceivable_a02dbbd7-bb79-46d0-af55-e8fe5cca4813" xlink:href="hto-20251231.xsd#hto_InterestIncomeOnIntercompanyNotesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_f5419d1b-8806-4af7-9701-a7965f01bd3d" xlink:to="loc_hto_InterestIncomeOnIntercompanyNotesReceivable_a02dbbd7-bb79-46d0-af55-e8fe5cca4813" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_39c5caf0-9c36-4951-bfba-88eea86d64b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_f5419d1b-8806-4af7-9701-a7965f01bd3d" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_39c5caf0-9c36-4951-bfba-88eea86d64b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_IncomeLossFromContinuingOperationsBeforeIncomeTaxesSubsidiaries_d4c90583-ef81-4b5d-8bf7-c16b0badd823" xlink:href="hto-20251231.xsd#hto_IncomeLossFromContinuingOperationsBeforeIncomeTaxesSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:to="loc_hto_IncomeLossFromContinuingOperationsBeforeIncomeTaxesSubsidiaries_d4c90583-ef81-4b5d-8bf7-c16b0badd823" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_5aed07bf-7c83-41e7-8931-94ea00257197" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_5aed07bf-7c83-41e7-8931-94ea00257197" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromSubsidiariesNetOfTax_46346716-49cb-4866-a5ae-59ee8ed5b2bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromSubsidiariesNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:to="loc_us-gaap_IncomeLossFromSubsidiariesNetOfTax_46346716-49cb-4866-a5ae-59ee8ed5b2bc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_39017edc-85aa-42ff-875c-21e20f6db39e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:to="loc_us-gaap_NetIncomeLoss_39017edc-85aa-42ff-875c-21e20f6db39e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_266dfa70-7ae5-4b02-bf0c-72fa09478f5a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_266dfa70-7ae5-4b02-bf0c-72fa09478f5a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_ede070a0-52a4-4ea0-8eb3-91ad34b1c959" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_0a0570d9-f049-48ce-ae52-5d22cf96f809" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_ede070a0-52a4-4ea0-8eb3-91ad34b1c959" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/FINANCIALSTATEMENTSCHEDULECondensedStatementsofCashFlowsDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#FINANCIALSTATEMENTSCHEDULECondensedStatementsofCashFlowsDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/FINANCIALSTATEMENTSCHEDULECondensedStatementsofCashFlowsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedFinancialStatementsCaptionsLineItems_97d38192-cc19-491f-b2c8-39f7a7f95beb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CondensedFinancialStatementsCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedFinancialStatementsTable_e0eb9f6a-a611-475f-8e92-ef32d9013ce0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfCondensedFinancialStatementsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_97d38192-cc19-491f-b2c8-39f7a7f95beb" xlink:to="loc_srt_ScheduleOfCondensedFinancialStatementsTable_e0eb9f6a-a611-475f-8e92-ef32d9013ce0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_69c67438-c24f-4da8-a300-8c4b25805842" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_e0eb9f6a-a611-475f-8e92-ef32d9013ce0" xlink:to="loc_srt_ConsolidatedEntitiesAxis_69c67438-c24f-4da8-a300-8c4b25805842" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_69c67438-c24f-4da8-a300-8c4b25805842_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_69c67438-c24f-4da8-a300-8c4b25805842" xlink:to="loc_srt_ConsolidatedEntitiesDomain_69c67438-c24f-4da8-a300-8c4b25805842_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_3a0c4943-14f3-4da0-b489-d5681e44c32a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_69c67438-c24f-4da8-a300-8c4b25805842" xlink:to="loc_srt_ConsolidatedEntitiesDomain_3a0c4943-14f3-4da0-b489-d5681e44c32a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ParentCompanyMember_d476c4ce-4067-4fdf-ad00-2478ae5ea14c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ParentCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_3a0c4943-14f3-4da0-b489-d5681e44c32a" xlink:to="loc_srt_ParentCompanyMember_d476c4ce-4067-4fdf-ad00-2478ae5ea14c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_905438b4-f7b2-4073-8eb0-a8bb5b1c71a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_97d38192-cc19-491f-b2c8-39f7a7f95beb" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_905438b4-f7b2-4073-8eb0-a8bb5b1c71a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_c13e195d-b4d3-41a0-bb69-615db04ea22e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_905438b4-f7b2-4073-8eb0-a8bb5b1c71a0" xlink:to="loc_us-gaap_NetIncomeLoss_c13e195d-b4d3-41a0-bb69-615db04ea22e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ae0834e0-22c3-4082-88a4-4b44ac0c0ed0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_905438b4-f7b2-4073-8eb0-a8bb5b1c71a0" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ae0834e0-22c3-4082-88a4-4b44ac0c0ed0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_EquityEarningsFromSubsidiariesNetOfTax_5a068153-c2e3-462d-96f8-6654e721be05" xlink:href="hto-20251231.xsd#hto_EquityEarningsFromSubsidiariesNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ae0834e0-22c3-4082-88a4-4b44ac0c0ed0" xlink:to="loc_hto_EquityEarningsFromSubsidiariesNetOfTax_5a068153-c2e3-462d-96f8-6654e721be05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_52e8a98a-b42a-410c-af5e-aa358216d22f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ae0834e0-22c3-4082-88a4-4b44ac0c0ed0" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_52e8a98a-b42a-410c-af5e-aa358216d22f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_782426b5-47d2-4aa1-9c0b-3a43e8e8c814" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ae0834e0-22c3-4082-88a4-4b44ac0c0ed0" xlink:to="loc_us-gaap_ShareBasedCompensation_782426b5-47d2-4aa1-9c0b-3a43e8e8c814" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_2fc57786-025d-4129-9762-a78e36247faa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ae0834e0-22c3-4082-88a4-4b44ac0c0ed0" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_2fc57786-025d-4129-9762-a78e36247faa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_b931bb80-f1a3-40e5-8c07-c0e247f82b42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_2fc57786-025d-4129-9762-a78e36247faa" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_b931bb80-f1a3-40e5-8c07-c0e247f82b42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_IncreaseDecreaseInIntercompanyReceivablesCurrent_b805deb0-7bf7-4e0c-8ff0-f492e3902ac7" xlink:href="hto-20251231.xsd#hto_IncreaseDecreaseInIntercompanyReceivablesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_2fc57786-025d-4129-9762-a78e36247faa" xlink:to="loc_hto_IncreaseDecreaseInIntercompanyReceivablesCurrent_b805deb0-7bf7-4e0c-8ff0-f492e3902ac7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedTaxesPayable_6ca09294-4e2e-4984-b4a2-cbd8a5660295" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInAccruedTaxesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_2fc57786-025d-4129-9762-a78e36247faa" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedTaxesPayable_6ca09294-4e2e-4984-b4a2-cbd8a5660295" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_ef1e1a1e-8e17-4c36-aef7-c5ca2f492361" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInInterestPayableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_2fc57786-025d-4129-9762-a78e36247faa" xlink:to="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_ef1e1a1e-8e17-4c36-aef7-c5ca2f492361" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ProceedsFromReturnOnCapitalFromInvestmentsInSubsidiaries_ba9f37c7-f7b1-4d99-bd47-c079dc340255" xlink:href="hto-20251231.xsd#hto_ProceedsFromReturnOnCapitalFromInvestmentsInSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_2fc57786-025d-4129-9762-a78e36247faa" xlink:to="loc_hto_ProceedsFromReturnOnCapitalFromInvestmentsInSubsidiaries_ba9f37c7-f7b1-4d99-bd47-c079dc340255" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_IncreaseDecreaseInLitigationSettlementNetOfLegalFees_9e051a83-d788-4880-a985-a6381baf648c" xlink:href="hto-20251231.xsd#hto_IncreaseDecreaseInLitigationSettlementNetOfLegalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_2fc57786-025d-4129-9762-a78e36247faa" xlink:to="loc_hto_IncreaseDecreaseInLitigationSettlementNetOfLegalFees_9e051a83-d788-4880-a985-a6381baf648c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_0fb42284-02b9-4893-8ab8-a0438a62a4a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_2fc57786-025d-4129-9762-a78e36247faa" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_0fb42284-02b9-4893-8ab8-a0438a62a4a4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7097a489-9aab-4045-8c59-baae5d2b37bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_905438b4-f7b2-4073-8eb0-a8bb5b1c71a0" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7097a489-9aab-4045-8c59-baae5d2b37bf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d4dbdb3e-aef3-4800-9763-c49cf2871831" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_97d38192-cc19-491f-b2c8-39f7a7f95beb" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d4dbdb3e-aef3-4800-9763-c49cf2871831" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PaymentsForNoteReceivablesFromSubsidiary_b5e18b67-65eb-4b5a-b62a-185d1bfd6018" xlink:href="hto-20251231.xsd#hto_PaymentsForNoteReceivablesFromSubsidiary"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d4dbdb3e-aef3-4800-9763-c49cf2871831" xlink:to="loc_hto_PaymentsForNoteReceivablesFromSubsidiary_b5e18b67-65eb-4b5a-b62a-185d1bfd6018" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ProceedsFromNoteReceivablesFromSubsidiary_9765a5b2-630e-4237-b795-5602d99c1eca" xlink:href="hto-20251231.xsd#hto_ProceedsFromNoteReceivablesFromSubsidiary"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d4dbdb3e-aef3-4800-9763-c49cf2871831" xlink:to="loc_hto_ProceedsFromNoteReceivablesFromSubsidiary_9765a5b2-630e-4237-b795-5602d99c1eca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates_6e9b4720-7db2-4845-9a0e-7ee5cb809062" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d4dbdb3e-aef3-4800-9763-c49cf2871831" xlink:to="loc_us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates_6e9b4720-7db2-4845-9a0e-7ee5cb809062" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_cbdfdd5e-66cc-4ef3-8f30-5c599e55579b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_d4dbdb3e-aef3-4800-9763-c49cf2871831" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_cbdfdd5e-66cc-4ef3-8f30-5c599e55579b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_4299fa3f-5690-4d6f-89ff-5dc0e9c9b9c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_97d38192-cc19-491f-b2c8-39f7a7f95beb" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_4299fa3f-5690-4d6f-89ff-5dc0e9c9b9c2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ProceedFromSubsidiaryNotesPayable_bc88e530-b139-4324-8154-3d81301bf418" xlink:href="hto-20251231.xsd#hto_ProceedFromSubsidiaryNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_4299fa3f-5690-4d6f-89ff-5dc0e9c9b9c2" xlink:to="loc_hto_ProceedFromSubsidiaryNotesPayable_bc88e530-b139-4324-8154-3d81301bf418" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_PaymentsForSubsidiaryNotesPayable_9471396c-a808-42d0-9d92-b4d22a4161f3" xlink:href="hto-20251231.xsd#hto_PaymentsForSubsidiaryNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_4299fa3f-5690-4d6f-89ff-5dc0e9c9b9c2" xlink:to="loc_hto_PaymentsForSubsidiaryNotesPayable_9471396c-a808-42d0-9d92-b4d22a4161f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_76ac690f-115e-4c13-9266-aed9169df05b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_4299fa3f-5690-4d6f-89ff-5dc0e9c9b9c2" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_76ac690f-115e-4c13-9266-aed9169df05b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_01447328-6ff2-40df-a7ea-74c90ba864e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_4299fa3f-5690-4d6f-89ff-5dc0e9c9b9c2" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_01447328-6ff2-40df-a7ea-74c90ba864e7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_a9a9a92e-1ba9-411a-baa5-7dbf44d836c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_4299fa3f-5690-4d6f-89ff-5dc0e9c9b9c2" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_a9a9a92e-1ba9-411a-baa5-7dbf44d836c9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ProceedsFromLitigationSettlementNetOfLegalFees_ab820822-6fd8-4aed-a90b-f629e7f8b528" xlink:href="hto-20251231.xsd#hto_ProceedsFromLitigationSettlementNetOfLegalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_4299fa3f-5690-4d6f-89ff-5dc0e9c9b9c2" xlink:to="loc_hto_ProceedsFromLitigationSettlementNetOfLegalFees_ab820822-6fd8-4aed-a90b-f629e7f8b528" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDebtIssuanceCosts_2543ae49-a8e4-41d7-a4b1-b1b3662c9fc6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsOfDebtIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_4299fa3f-5690-4d6f-89ff-5dc0e9c9b9c2" xlink:to="loc_us-gaap_PaymentsOfDebtIssuanceCosts_2543ae49-a8e4-41d7-a4b1-b1b3662c9fc6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividendsCommonStock_4101d120-b77f-477d-a4dc-2f841e064ff3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsOfDividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_4299fa3f-5690-4d6f-89ff-5dc0e9c9b9c2" xlink:to="loc_us-gaap_PaymentsOfDividendsCommonStock_4101d120-b77f-477d-a4dc-2f841e064ff3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_4f87c824-df1a-44af-a85a-0cfb605c3276" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_4299fa3f-5690-4d6f-89ff-5dc0e9c9b9c2" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_4f87c824-df1a-44af-a85a-0cfb605c3276" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_45cfcafc-9582-487a-a945-af03ef14e8cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_97d38192-cc19-491f-b2c8-39f7a7f95beb" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_45cfcafc-9582-487a-a945-af03ef14e8cf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_79a39148-4f13-4765-abf4-790edf08db41" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_97d38192-cc19-491f-b2c8-39f7a7f95beb" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_79a39148-4f13-4765-abf4-790edf08db41" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_f6d6398d-24a7-41de-bd5f-97603f96090d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_86a99028-d02d-4e6c-88ec-49cb21f127ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SupplementalCashFlowInformationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_97d38192-cc19-491f-b2c8-39f7a7f95beb" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_86a99028-d02d-4e6c-88ec-49cb21f127ad" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_1435e7a6-de6f-4bbc-86ac-acaba06469a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_86a99028-d02d-4e6c-88ec-49cb21f127ad" xlink:to="loc_us-gaap_InterestPaidNet_1435e7a6-de6f-4bbc-86ac-acaba06469a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_fd1dacf4-9520-44b7-98bd-c8ffc3966919" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_86a99028-d02d-4e6c-88ec-49cb21f127ad" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_fd1dacf4-9520-44b7-98bd-c8ffc3966919" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_81a4c734-c9bf-4181-b0cc-428db00fda58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_97d38192-cc19-491f-b2c8-39f7a7f95beb" xlink:to="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_81a4c734-c9bf-4181-b0cc-428db00fda58" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_ShareBasedCompensationFromInvestmentInSubsidiaries_af67d58e-d684-47bf-a52d-52df1117e2a5" xlink:href="hto-20251231.xsd#hto_ShareBasedCompensationFromInvestmentInSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_81a4c734-c9bf-4181-b0cc-428db00fda58" xlink:to="loc_hto_ShareBasedCompensationFromInvestmentInSubsidiaries_af67d58e-d684-47bf-a52d-52df1117e2a5" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/FINANCIALSTATEMENTSCHEDULEScheduleofPrincipalPaymentsonLongTermDebtDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#FINANCIALSTATEMENTSCHEDULEScheduleofPrincipalPaymentsonLongTermDebtDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/FINANCIALSTATEMENTSCHEDULEScheduleofPrincipalPaymentsonLongTermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedFinancialStatementsCaptionsLineItems_fbe4a132-08b9-4cbe-a04f-6b842649008d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CondensedFinancialStatementsCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedFinancialStatementsTable_ac2d0c35-8f36-4b51-a0c2-823516b3a04f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfCondensedFinancialStatementsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_fbe4a132-08b9-4cbe-a04f-6b842649008d" xlink:to="loc_srt_ScheduleOfCondensedFinancialStatementsTable_ac2d0c35-8f36-4b51-a0c2-823516b3a04f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_9473bb7c-98b0-44c0-9086-cc10792de551" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_ac2d0c35-8f36-4b51-a0c2-823516b3a04f" xlink:to="loc_srt_ConsolidatedEntitiesAxis_9473bb7c-98b0-44c0-9086-cc10792de551" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_9473bb7c-98b0-44c0-9086-cc10792de551_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_9473bb7c-98b0-44c0-9086-cc10792de551" xlink:to="loc_srt_ConsolidatedEntitiesDomain_9473bb7c-98b0-44c0-9086-cc10792de551_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_de09ca64-a764-4a34-b105-abf76cbae87b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_9473bb7c-98b0-44c0-9086-cc10792de551" xlink:to="loc_srt_ConsolidatedEntitiesDomain_de09ca64-a764-4a34-b105-abf76cbae87b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ParentCompanyMember_33b78b30-b079-4dc5-b174-a6cd74cb5139" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ParentCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_de09ca64-a764-4a34-b105-abf76cbae87b" xlink:to="loc_srt_ParentCompanyMember_33b78b30-b079-4dc5-b174-a6cd74cb5139" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_395a49b9-4139-4c8e-82f6-188c0ded2a98" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_fbe4a132-08b9-4cbe-a04f-6b842649008d" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_395a49b9-4139-4c8e-82f6-188c0ded2a98" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_cbea3e56-8541-433a-a2ba-d002a268f093" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_fbe4a132-08b9-4cbe-a04f-6b842649008d" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_cbea3e56-8541-433a-a2ba-d002a268f093" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_d8e6baa7-e576-467f-9423-6574472cea73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_fbe4a132-08b9-4cbe-a04f-6b842649008d" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_d8e6baa7-e576-467f-9423-6574472cea73" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_3ab8a708-3dae-43d7-8232-44ecbe004594" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_fbe4a132-08b9-4cbe-a04f-6b842649008d" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_3ab8a708-3dae-43d7-8232-44ecbe004594" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_d4076aa3-a1eb-4934-bee4-4e01530763d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_fbe4a132-08b9-4cbe-a04f-6b842649008d" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_d4076aa3-a1eb-4934-bee4-4e01530763d4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_0c9ab0f7-1ffa-4889-b0d4-63a616a70281" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_fbe4a132-08b9-4cbe-a04f-6b842649008d" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_0c9ab0f7-1ffa-4889-b0d4-63a616a70281" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.h2o-america.com/role/VALUATIONANDQUALIFYINGACCOUNTSANDRESERVESDetails" xlink:type="simple" xlink:href="hto-20251231.xsd#VALUATIONANDQUALIFYINGACCOUNTSANDRESERVESDetails"/>
  <link:definitionLink xlink:role="http://www.h2o-america.com/role/VALUATIONANDQUALIFYINGACCOUNTSANDRESERVESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_ValuationAndQualifyingAccountsDisclosureLineItems_9798aed4-f604-4bbe-92ad-7e8d491bee04" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ValuationAndQualifyingAccountsDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ValuationAndQualifyingAccountsDisclosureTable_5bc89fad-eaf7-411a-9905-f4b01f30afc8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ValuationAndQualifyingAccountsDisclosureTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_ValuationAndQualifyingAccountsDisclosureLineItems_9798aed4-f604-4bbe-92ad-7e8d491bee04" xlink:to="loc_srt_ValuationAndQualifyingAccountsDisclosureTable_5bc89fad-eaf7-411a-9905-f4b01f30afc8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_39ddf2ac-9abb-464c-a8f4-27bc2ddf83da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ValuationAndQualifyingAccountsDisclosureTable_5bc89fad-eaf7-411a-9905-f4b01f30afc8" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_39ddf2ac-9abb-464c-a8f4-27bc2ddf83da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDomain_39ddf2ac-9abb-464c-a8f4-27bc2ddf83da_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_39ddf2ac-9abb-464c-a8f4-27bc2ddf83da" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDomain_39ddf2ac-9abb-464c-a8f4-27bc2ddf83da_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDomain_5bb1cbae-4850-4888-b5a7-f68ef5072221" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_39ddf2ac-9abb-464c-a8f4-27bc2ddf83da" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDomain_5bb1cbae-4850-4888-b5a7-f68ef5072221" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForCreditLossMember_b22ea767-eb19-4ff6-a9a5-97b4859d92ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllowanceForCreditLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesDomain_5bb1cbae-4850-4888-b5a7-f68ef5072221" xlink:to="loc_us-gaap_AllowanceForCreditLossMember_b22ea767-eb19-4ff6-a9a5-97b4859d92ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LegalReserveMember_42ac7525-cb71-42a3-a11e-6185a42a9ca3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LegalReserveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesDomain_5bb1cbae-4850-4888-b5a7-f68ef5072221" xlink:to="loc_us-gaap_LegalReserveMember_42ac7525-cb71-42a3-a11e-6185a42a9ca3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_09337934-e994-4b54-b7c5-8d39ca30a85b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MovementInValuationAllowancesAndReservesRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ValuationAndQualifyingAccountsDisclosureLineItems_9798aed4-f604-4bbe-92ad-7e8d491bee04" xlink:to="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_09337934-e994-4b54-b7c5-8d39ca30a85b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesBalance_b8e7bc9d-897e-4aef-a707-9ada0ae3c9fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_09337934-e994-4b54-b7c5-8d39ca30a85b" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesBalance_b8e7bc9d-897e-4aef-a707-9ada0ae3c9fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense_21e17894-dc39-44fb-af7e-9b94b6d10414" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_09337934-e994-4b54-b7c5-8d39ca30a85b" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense_21e17894-dc39-44fb-af7e-9b94b6d10414" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hto_SECSchedule1209ValuationAllowancesAndReservesChargedToRegulatoryAssets_3a756381-9a6c-4e6c-ac9c-12916bb8dab5" xlink:href="hto-20251231.xsd#hto_SECSchedule1209ValuationAllowancesAndReservesChargedToRegulatoryAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_09337934-e994-4b54-b7c5-8d39ca30a85b" xlink:to="loc_hto_SECSchedule1209ValuationAllowancesAndReservesChargedToRegulatoryAssets_3a756381-9a6c-4e6c-ac9c-12916bb8dab5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDeductions_5b73d200-fbdd-48a0-8a9e-8df98ff69a15" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesDeductions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_09337934-e994-4b54-b7c5-8d39ca30a85b" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDeductions_5b73d200-fbdd-48a0-8a9e-8df98ff69a15" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesRecoveries_4a7f922a-6574-4071-bb74-b736dfa175bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesRecoveries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_09337934-e994-4b54-b7c5-8d39ca30a85b" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesRecoveries_4a7f922a-6574-4071-bb74-b736dfa175bf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesAdjustments_03c01cb3-ba2b-43a2-9ce1-2303e2e4d2c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_09337934-e994-4b54-b7c5-8d39ca30a85b" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesAdjustments_03c01cb3-ba2b-43a2-9ce1-2303e2e4d2c5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesBalance_645a4fa6-c8f0-46ec-948b-1a29973228ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesBalance"/>
  </link:definitionLink>
</link:linkbase>
