Reserve water tank systems are useful in areas of Africa, where running water is available, but often cut off for days and weeks at a time. The set up involves mounting a water tank on a stand, wall or roof, connecting existing water pipes to the top of the tank and filling the tank when the tap water is running. Piping from the bottom of the tank is used for gravity-assisted outflow of water for everyday use when the tap water is cut off. These systems are low in cost, easy to set up and can provide a reliable source of clean water to a lot of people. The cost is typically between $2000-$5000 depending on the size of the tank and type of mounting.