Most motorhomes contain a water system for supplying cold (and hot) water for use in the sinks or shower. This can range from something as simple as a submersible pump in a water can or a fully plumbed pressurised system.
Generally the motorhome will contain a fresh water tank and a waste water tank (grey water). Waste from the toilet (black water) is kept separately. Having the tanks inside the motorhome avoids the possibility of the water freezing in winter. If either tank is mounted outside and underneath the floor, then some means must be provided to prevent freezing. This can be done by surrounding the tank with an insulated cavity which is fed with warm air from the heating system or with a small electric immersion heater.
Usually a gauge of some description is provided to monitor the water level the tanks. Growth of algae on the sensing probes can lead to erroneous readings. It is usually possible to withdraw or access the sensor for cleaning.
Normally the toilet has its own separate water supply with which a proprietary additive can be mixed. Some motorhomes have the toilet fed from the general cold water system which is undesirable because of the potential of back contamination.
Electric water pumps are usually of either the submersible type or the inline type. The inline type usually provides the best performance in terms of pressure and flow rate. Both types are powered from the leisure battery. Some motorhomes are provided with a microswitch at each tap which activates the pump when the tap is opened. Faulty microswitches are a common cause for complaint. The alternative is where the water pump is controlled by pressure switch which automatically senses the drop in pressure when a tap is opened and activates the pump. An accumulator (like an expansion vessel) may be included in such a system.