This paper presents the first detailed long-​​term stock turnover model to inves­ti­gate sce­nar­ios to decar­bonize the res­i­den­tial water heat­ing sec­tor in Cal­i­for­nia, which is cur­rently dom­i­nated by nat­ural gas. We model a mix of water heat­ing (WH) tech­nolo­gies includ­ing con­ven­tional and on-​​demand (tank-​​less) nat­ural gas heat­ing, elec­tric resis­tance, exist­ing elec­tric heat pumps, advanced heat pumps with low global warm­ing refrig­er­ants and solar ther­mal water heaters. Tech­ni­cally fea­si­ble pol­icy sce­nar­ios are devel­oped by con­sid­er­ing com­bi­na­tions of WH tech­nolo­gies with effi­ciency gains within each tech­nol­ogy, low­er­ing global warm­ing poten­tial of refrig­er­ants and decreas­ing grid car­bon inten­sity. We then eval­u­ate energy demand, emis­sions and equip­ment replace­ment costs of the path­ways. We develop mul­ti­ple sce­nar­ios by which the annual green­house gas emis­sions from res­i­den­tial water heaters in Cal­i­for­nia can be reduced by over 80% from 1990 lev­els result­ing in an annual sav­ings of over 10 Mil­lion Met­ric Tons by 2050. The over­all cost of tran­si­tion will depend on future cost reduc­tions in heat pump and solar ther­mal water heat­ing equip­ment, energy costs, and hot water consumption.