The water tank and pump, actually a new Harbor Freight 14 gallon sprayer w/12v DC pump, will only run on demand. If there is no water demand the system will stay pressurized, and the pump will not run. There is a switch that controls the pump in the galley inside roof just to the left of the overhead light. This way, the system can be shut off when sleeping to prevent an inadvertent leak from draining the system.