A storage water heater is a domestic water heating appliance that uses a hot water storage tank to maximize heating capacity and provide instantaneous delivery of hot water. Conventional storage water heaters use a variety of fuels, including natural gas, propane, fuel oil, and electricity. Less conventional water heating technologies, such as heat pump water heaters and solar water heaters, can also be categorized as storage water heaters. Conventional storage water heaters are the most common water heating type used in the United States.