Water supply & drainage system

water supply drains london system

The diagrams for typical household pipe systems for the two principal forms of water supply and drainage found in the United Kingdom and London. Both supply systems may be found with either one of the drainage systems. (Pipes for central heating, are not shown.) The details of the piping will vary from house to house according to the location of appliances, but the main features are constant. Track the layout of the pipes in your own home before you attempt any repairs or alterations.

The supply system may be either direct or indirect.

In the direct type, the mains water is conducted through the vertical pipe known as the rising main straight to the cold taps and appliances throughout the house; in the indirect system, the rising main fills a cold water storage cistern located above the hot water cylinder-usually in the roof space-and water is then drawn from the cistern to supply the needs of the household. In this scheme, the law requires that one tap (usually in the kitchen) should always be supplied direct from the mains, so that the occupants can drink water that has not been exposed to airborne bacteria while stored in the cistern.

A second mains tap is permitted but not required; all others must be drawn from the cistern. The service pipe by which the water supply enters the house from the public water main is controlled by a stoptap designed to act also as a non-return valve. This is a precaution against the accident of back-siphonage, whereby an unexpected drop in mains pressure might, in unusual circumstances, allow contaminated water from an appliance within the house to be siphoned back into the mains, where it could pollute the supply. If the stoptap is outside the boundary of the property, it belongs to the water authority; if inside, it is the householder’s responsibility. Just inside the house is usually another stoptap, with which the owner can interrupt the flow into the household system, for instance before dealing with a leak.
It is useful to have stoptaps and valves at other points in the system as well, so that you can isolate and drain different sections of piping when you want to work on them. The drainage system may be either the single-stack type , in which W.C.s and all other appliances empty into the same soil and waste stack, or double-stack, where the soil stack for sewage is separate from the waste stack for water from baths, basins and sinks. All soil stacks, whether separate or combined, have a vent above roof level, to keep air flowing through the system. So that the sewers will not be overburdened by sudden storms, surface water-rain-sometimes flows through gutters and a trapped gully into a separate drain.

The direct system.
In a direct supply system, the cold water storage cistern feeds only the hot water cylinder, while all the cold taps, W.C. cisterns and other appliances are supplied under mains pressure. The double-stack drainage system, common in older houses, has a soil stack carrying sewage and a separate waste stack for to other household wastes, both positioned against the external wall of the house. They are usually constructed of cast iron, but many have been replaced by PVC at some time when they needed repair. The waste stack can be an open hopper head, but it could also be a sealed pipe, vented at roof level, like the soil stack.

The indirect system.
In a typical indirect supply system, only the kitchen cold tap and a garden tap are connected direct to the mains. The remaining taps and appliances, and the hot water cylinder, are fed from the cold water storage cistern. The single combined soil and waste stack, normally built of PVC piping, is located inside the house. The water from the kitchen sink is shown discharging into its own trapped gully; however, it might equally well feed into the main stack like the rest of the appliances in the house.