Emergency Advice*.
If you have water leaking now, you may want to cut off your supply. Here's how:
(If you don't have a leak, it's worth reading this so that you know what to do in an emergency.)
Cutting off the water supply to your entire property:
It is quite easy to cut off the supply; turn off the stop valve located where your supply enters the property - usually located under your kitchen sink, or sometimes in a cupboard near the front door. (The stop valve will look something like the one in the photo on the right.)
If it is stiff, try holding the tap head with a dry cloth to gain extra grip. Don't over-force it, for example using pliers - you may make a bad situation worse!
It is a good idea to switch off you heating & hot water at the same time.
If this doesn't stop the leak don't panic - your system is most likely fed from a tank in the loft.
In many UK properties all of the hot taps, and the upstairs cold taps are fed via a loft tank. There should be either taps or valves available to turn off. These are most likely to be next to the cold water tank in the loft, or possibly in your airing cupboard. Turn these off, then switch on the taps until the water flow has stopped. (Flushing the loo will help you empty the loft tank if you're really stuck). If you are unsure as to which taps in your loft are the correct ones, it's essential that your heating & hot water remain turned off & that you call a plumber ASAP.
Frozen or burst Pipes:
If you can see a split in a frozen pipe, act quickly: cut your supply off & call a plumber. In the meantime you may be able to make a temporary repair with self amalgamating tape - ask at your local DIY store. This may help keep you dry while waiting for the plumber to arrive.
Closing your outdoor Stopcock:
Rarely needed, but good to know it's location so that you can tell your plumber. You'll find it outside of your property, near a boundary wall, under a 6-inch-square cover.
Turning off requires a stopcock key, but anyone who needs to turn it off should have one. As it's outdoors in the street, bear in mind that the void between the cover & the stopcock could contain sharp or dangerous objects.
*Emergency advice should always be followed with caution. All plumbing work should be carried out by a competent person. If this advice is followed, it is at your own risk, and is provided without warranty. CFRP accepts no liability for any loss as a result of you following this free advice. If in doubt, consult a competent person.