Each one of us uses about 160 liters (35 gallons) of water a day, and takes it for granted. Only in a long spell of dry weather comes awareness that we should use it carefully. Our use is controlled by the supply system — this is how it works.

In the last 50 years the consumption of water has almost doubled. Rising standards of living have given rise to increased consumption, and a greater awareness of the need for hygiene has also played a large role in increasing the demand. Faced with this high demand, supply sources have been hard pressed to keep up. Understanding Water Supply Where it comes from Water is supplied by the local water authority (or the Undertaking as it is known in the plumbing trade). After falling as rain it is collected in reservoirs which are ted by streams and rivers, or is pumped from underground wells. Water varies a lot in its chemical makeup since it picks up minerals and gases as it flows, If it picks up calcium, magnesium and sodium salts it will be hard – the menace of pipe systems. Before being distributed it is usually filtered through said and pebble beds to remove solids and organisms, and may have chlorine added to it to ensure that it is ‘potable’ — drinkable. Fluoride is also sometimes added for the protection of teeth. Distribution is carried out by a network of pipes starting with ‘trunk mains’ which may be as much as 61 0mm (24in) in diameter. These split into mains and sub-mains which run underneath streets and side streets. It is these sub-mains which are tapped by individual houses for their supply. The house system may be ‘direct’ in which all cold water supplies are piped direct from the rising main, with the cistern only being used to supply the hot water tank. Or it may be an ‘indirect’ system in which all coldwater supplies are taken from the cistern, with the exception of a direct supply to the kitchen sink for drinking purposes. For water to flow through the trunk mains — and eventually into your house — it must be under a certain amount of pressure. This pressure is assisted by pumps but it is vital that somewhere in the mains system the water should reach a height in a reservoir or water tower, higher than any domestic system it has to supply.

The vertical distance through which the water ‘falls’ is known as the ‘pressure head and without it our cisterns would never fill up without a lot of expensive additional pumping. The storage cistern also provides a pressure head inside the house, which is why it’s preferable to have it in the roof space.