Rising main and water service

Frequently asked questions

Where does the utility's pipe stop and the owner's begin?

At the boundary, and the words either side of that point are different. In British usage the COMMUNICATION pipe runs from the water main in the street to the boundary stop tap, and it belongs to the water company; the SERVICE pipe runs from there to the property and belongs to the owner. So a leak in the road is the company's and a leak under the front garden is usually the owner's, which is why the outside stop tap is worth finding before it is needed rather than after. American usage puts the same boundary at the curb stop, and Canadian at the same place with the same name. The practical point for anyone reading a report across markets: main means the street in America and the incoming pipe in Britain, and the difference is whose bill it is.

Why does a single kitchen tap have to be fed directly from it?

Because it is the drinking water point, and older British systems stored cold water in a loft cistern. A traditional indirect system fed the bathroom, the WC and the hot water cylinder from an open tank in the roof — water that sat in an accessible vessel, warmed in summer, and was open to whatever entered the loft. The kitchen tap was therefore taken straight off the rising main before any of that, so there was one outlet of water fit to drink. That convention survives in the regulations and in the plumbing habits of the country long after most houses became directly fed by a combi. Anybody working on an older system needs to know it, because reconnecting a kitchen tap to a stored supply is a regulatory breach and not merely a preference.

What size should it be, and why is the answer usually flow rather than pressure?

Sized on the flow the property needs and the pressure available to deliver it, and the constraint is almost always a long run of undersized pipe rather than the pressure at the main. Pressure at the street is generally adequate; what it has to survive is the resistance of everything between there and the tap, and that resistance rises steeply as diameter falls — halving the bore multiplies the loss many times over for the same flow. So a house with poor flow at the top floor very often has a modern boiler, an adequate street pressure, and a fifty-year-old service pipe of small diameter running thirty metres from the road. Replacing the last few metres inside the house changes nothing; the run is the problem, and measuring the flow rate at the outside stop tap is what separates the two.