The on-board water heater provides hot water for faucets at the kitchen, bathroom, shower, and on some models the washing machine. Typically smaller rigs have a 6 gallon heater that is powered by LP and the 12-volt system. 6 gallons doesn’t go far so water conservation becomes a must. An upgrade is the 10 gallon Electric/LP model that provides enough hot water to take a good long shower! Not much maintenance is required, however it’s import to drain the water heater when winterizing!