Path = Home : Repairing Household Plumbing > The Domestic Cold Water Supply

The Domestic Cold Water Supply

Your local water company (Thames Water, Yorkshire Water etc.) is responsible for supplying your house with water and for the disposal of the waste water and sewage.

How the water gets to your home

Water is collected in large reservoirs where many of the impurities can settle out. It is then strained into large tanks to allow more sedimentation. Next, it is filtered through sand beds before chlorine and ammonia are added to make the water pure enough for drinking. Finally, the water is put in storage reservoirs. When it is required, the water runs along secondary mains and then into street mains.

A communication pipe (one for each house) comes from the street mains and connects to the water company's stopvalve. Normally, there is a metal inspection plate outside the front of your house which covers the water meter (if you have one) and the water company's stopvalve controlling the flow of water to your house. Everything after this valve is your responsibility (which means if anything goes wrong with the plumbing after the stopvalve, the water company doesn't have to fix it - you do).

From the stopvalve the water travels along a service pipe to reach your house. The service pipe is run 750 to 900mm (30 to 36in) below the surface of the ground to protect it from frost damage and being damaged by garden tools. It is also covered by an earthenware sleeve to protect it as it passes through the foundations of the house. The service pipe should be insulated where it passes up through the sub-floor cavity into the house to become the rising main.

Near to where it has entered the house, there shouId be another stopvalve. Usually it is under the kitchen sink, though it could be under the stairs. It is important that you know where this valve is located because it will enable you to turn off the water supply in an emergency, such as a burst pipe. Some older houses have an underground stopcock just outside the house which can be operated by a long metal key.

The direct cold water system

In many older houses water at mains pressure is supplied directly to all the cold water taps and toilets. This means that all the cold water system is under high pressure. The only advantage with the direct system is that drinking water can be taken from any cold water tap in the house.

The indirect cold water system

Modern houses, are plumbed with an indirect water system. Water under mains pressure enters the house through a service pipe and travels via the rising main directly to the cold water storage tank. Because the water flows under the pressure of gravity, the tank needs to be higher than any of the outlets it is to supply. For this reason it is usually located in the loft, although it can be combined with a hot water cylinder.

For hygiene reasons, the cold tap in the kitchen sink is supplied with cold water direct from the rising main. Washing machines and dishwashers are often connected to this too, as it makes the plumbing installation simpler. The hot water storage cylinder is supplied with cold water from the cold water storage tank.

This indirect cold water system has a number of advantages, the most important one is that there's a reservoir of water available in the cold water tank which can still be used to supply the taps and toilets if the mains supply is temporarily cut off. It also means that domestic water is supplied at a lower pressure than the mains supply, which helps reduce wear and tear on the system (high mains pressure can cause 'water hammer' as the water tries to flow around tight bends in the pipes).