The Service Pipe And Branch Supply Pipes

The service pipe continues under the wall near the kitchen sink, which means that it is often attached to the inner face of the outside wall. This is contrary to the recommendation that it should be attached to an inside wall, and so such a pipe should be lagged with insulation material.

The pipe should also be insulated if it comes through any sub-ground floor cavity where it would be subjected to the icy blasts of winter from under-floor ventilation. Again these precautions are both intended to minimize the risk of frost damage. When the service pipe rises above the ground floor it is called the ‘rising main’ and it eventually terminates in the supply cistern, which is usually in the roof cavity. The householder’s main stop-valve is usually found on the rising main a little way above floor level. This is the most important tap’ in the house. In any plumbing emergency — when bursts or leaks occur, for example, your first action should be to turn this tap off, thus isolating the house system from the mains water supply. The stop-valve should always be turned off when you go away if the house is going to be empty. In old houses the location of the stop- valve may vary considerably, it may be in the cellar, under the stairs, or even under a cover beneath the front path — or it may not exist at all, in which case the authority’s stop-valve is the only control. Branch supply pipes At least one ‘branch’ supply pipe eaves the rising main close above the stop-valve and drain tap — this is to the tap over the kitchen sink. This tap must be supplied direct from the main supply as it is supposed to provide all drinking and cooking water. Water which has been in a storage cistern is no longer considered drinkable, sometimes termed ‘potable’, as it may be slightly contaminated by debris in the storage cistern. Other branches may be taken at this point to an outside tap. or to a washing machine or dishwasher. The rising main continues upwards and while its ultimate destination is the cold water storage cistern the pipework in between will vary from house to house, depending on whether a ‘direct’ or ‘indirect’ system has been installed. In many areas indirect systems must be installed in new buildings, yet in Western Europe direct systems are the rule. Indirect systems have been encouraged because of the difficulty in maintaining constant mains pressure particularly at times of peak demand.


Routing of most supplies through the storage cistern evens out fluctuations, and it also rules out the risk of ‘back siphonage whereby dirty water could be sucked back into the mains supply — though this rarely occurs. The 1976 drought in the UK provided good reason for indirect systems, since each house had an emergency supply in the storage cistern if the mains water had to be shut off.