RV water systems use either an electric water pump connected to an onboard fresh water tank or a municipal water supply to feed water to the RV's sink, toilet and shower. Waste water is stored in separate tanks for later disposal.
RV water systems rely on a fresh water source for proper operation. Some RV's are equipped with a fresh water tank that is filled before use. Fresh water sources are fed to the RV with a one-way valve that prevents water from re-entering the supply source. A 12-volt water pump moves fresh water from the supply source to water outlets, such as faucets and hose hook-ups, as well as the water heater. When a water outlet is in the open position, the water pump is activated and creates the pressure necessary to allow water to flow freely.
Used water from the sink and shower is drained into a storage tank known as the grey water tank. Grey water is any waste water that is not contaminated with human waste. Grey water is commonly disposed of in wooded areas or into a municipal or campground sewer system. Black water, which is water contaminated with human waste, from the toilet is stored in the black water tank. The black water tank must be dumped at an approved RV dump site.