Abstract: A water system for a mobile vehicle has an intermittent external source of water and uses water from an internal storage tank to provide a continuous supply of water. A water storage refill system automatically refills the internal storage tank whenever there is an external source of water. An inlet conduit is detachably connectable to an external water supply and in communication with the internal storage tank and the remainder of a plumbing system. An electrically actuated valve in the inlet conduit controls the flow of water from the external source of water to the internal storage tank in response to sensing devices indicating the need for water in the storage tank and the availability of water from the external water source.