How Water Systems Work
All domestic water is supplied by a service pipe connected to the water main in the road. The internal layout varies according to how water is distributed and heated.
In most homes, cold water used to be supplied indirectly. All the cold water outlets except the kitchen sink are fed from a storage tank (cistern).
This has several advantages:
♦ The tank provides an emergency supply if the mains get cut off.
♦ There is no direct link between appliances and the rising main (apart from the kitchen sink), reducing the chance of contaminated waste water being siphoned back into the mains.
♦ Water fed from the tank is well below mains pressure, reducing the chance of noisy pipes.
However, there are drawbacks:
♦ Only the kitchen cold tap should be used for drinking. Cold storage tanks can become contaminated.
♦ The water pressure in the pipes fed by the storage tank relies on gravity, so the tank must be high enough above the outlets for the water to discharge at a sensible rate. This is not always easy to arrange, particularly in flats.
♦ The storage tank is usually in the roof, where frost may damage it.
In direct systems (increasingly common) all the cold water outlets are supplied directly from the rising main. The main advantages are simpler, cheaper plumbing, the use of every cold tap for drinking, and no problems of insufficient pressure.
The hot water supply
This depends on the type of heating installed.
Most houses have what is called a vented system, in which water is fed to the heater from a storage tank, and a vent pipe leading back to the tank helps to accommodate expansion of the water as it gets hot. In an indirect, the cold water storage tank can be used for this. But in a direct cold water system, a vented hot water system has to have its own storage tank, no matter how the other cold outlets are supplied.
In an unvented hot water system, the water heater is supplied direct from the rising main and special valves regulate the incoming water pressure. There is no vent pipe. Instead, expansion of the water as it gets hot is accommodated by the heater itself, or by a separate sealed expansion vessel; there are also various safety devices to stop the water boiling and guard against pressure build-up.
Each system has its. Vented systems need more pipework, plus space for a storage tank, but contain relatively few mechanical components. Unvented systems have more to go wrong, but offer greater design flexibility and in many cases better performance; they don’t require a storage tank, so are less vulnerable to frost.