Cold water supply pipes connected directly to the mains
In the UK these pipes usually only supply the kitchen cold tap, the cold water storage tank and sometimes instantaneous water heaters. In Australia and other countries, the pipes may supply all cold water taps and the hot water storage cylinder. The simple way of deciding whether any pipe or tap is supplied directly by the mains is by the pressure – taps supplied from a tank are what’s known as gravity-fed and the pressure of water is relatively low compared to mains pressure.
To turn off the water, look for the mains stop-valves. There may, in fact, be two: one inside the house where the mains pipe enters (under the kitchen sink, in the utility room, or even under the stairs); the other outside – either just inside the boundary of the property (near to a water meter, if you have one), or under the footpath outside the garden fence.
Outdoor stop-valves may be set as much as a metre (3 ft) down beneath a hinged cover or metal plate, and you may need a special ‘key’ which is really just a long rod with a square socket on the end which fits over the tap to turn it. In most cases, however, it’s simply a matter of reaching down to turn it off by nana or with a wrench. Some outdoor stop-valves also control a neighbour’s water supply, so do warn them if you’re turning it off. The stop-valve inside will either be a wheel type or an ordinary T-shaped type.
The only possible complication is if it hasn’t been touched for years and is stuck fast. A little penetrating oil and tapping it with a hammer will usually loosen it sufficiently. (It’s worth closing the stop-valve now and again to see that it doesn’t get stuck.)
Cold water supply pipes from a cold water storage tank
In the UK these pipes usually supply the bathroom cold taps, the WC cistern and the hot water cylinder. To close off the water supply in these pipes there’s often a stop-valve immediately alongside the cold water tank where the pipe exits. Turn this off first and then open all cold water taps. They’ll run dry almost immediately. If there isn’t a stop-valve, you have to drain the whole tank. So first you stop water entering the tank by either turning off the mains (as above) or by tying up the ball-valve in the tank so that it remains closed. Then you open all the taps in the house.
Hot water pipes
These are all supplied from a hot water cylinder, which in turn gets its cold water either from the cold tank or from the mains. Since hot water leaves the hot water storage cylinder from the top, it’s only the pressure of water going in at the bottom of the cylinder that forces the water out. Turn off the supply of cold water (either at the cold water tank, or at the mains) and you stop the flow. In this sort of situation the hot water cylinder remains full. If for any reason you need to drain this as well, use the drain cock near the bottom. It’s essential in this case to turn off either the immersion heater or boiler.