Cold- and hot-water storage, expansion of materials, Boyle's and Charles' laws

Because a storage system reduces pressure fluctuations, thermostatic mixing valves for showers, etc., operate more efficiently. The reduction o f pressure reduces the risk o f noise from water hammer and there is less wear on the valves. The air gap between the ballvalve and the water level in the storage cistern prevents water being drawn back into the main, due to ‘back siphonage’.