The water supply is pumped through the mains to your home – but the story doesn’t end there. You must have a storage tank in order to keep an amount of water in reserve, and distribution pipes to feed it around the home. The cold water storage cistern eases immediate demand on the mains during peak periods, such as first thing in the morning when large quantities of water are used for baths and toilet flushing. The cistern will refill slowly, then more quickly as demand on the mains drops. The storage cistern also provides a reserve of water against possible shut-down of the mains. When water is cut off for a few hours for mains repairs, you need only draw off in advance sufficient water for drinking and cooking; the cistern will keep the hot water system, bath taps and toilet operating. It will also provide a supply of water under constant, relatively low pressure for a cylinder storage hot water system. Although available in various capacities, most water authorities stipulate a maximum of fifty gallons for storage cisterns. They are now usually made of plastic materials, although galvanized steel are still found.
The cistern is normally situated in the loft and sometimes in the upper part of an airing cupboard. The loft is the best place, since it allows the maximum amount of fall from the cistern; water is supplied under great pressure, ensuring a strong flow at the outlets. Since the full cistern will be heavy, it is usually placed over a dividing wall and if possible, as a frost precaution, against a smoke-duct in constant use. The supply of water to the cistern from the rising main is controlled by a ball valve which shuts off water when the cistern is full. A warning pipe extending outside the house and acting as an overflow is connected near the top of the cistern to indicate when the ball valve is faulty. This pipe must be of at least twenty-two mm diameter and should be set at a slight fall to ensure a continuous flow of water. There are also two distribution pipes, usually fitted near the bottom of the cistern: one serves the bathroom cold tapes and the toilet cistern, the other supplies the hot water storage cylinder. A vent pipe from the top of the hot water cylinder is positioned over the cistern. This allows air to escape when the cylinder is filling up. It should never enter the water as this would cause hot water to be siphoned into the cold cistern.