Search for the main stop cock or stop valve of the house to turn off the main water supply. It is usually located under or near the kitchen sink. Turning this off will only isolate those parts of the system which are mains or direct supplies.
Water can be supplied indirectly by a water storage cistern for appliances and outlets such as bathroom taps and toilets. To turn off the water coming from the water storage cistern you will need to shut off the valve on the cistern’s outlet supply.
The hot water in your home may be direct feed or indirect feed. If you have a combi boiler, then the hot water is supplied direct and closing the mains stop valve will close off the water. If you have a hot water cylinder, this will be an indirect supply. There will be a valve on the pipe from the cold water storage cistern to the hot water cylinder. Closing off this valve will stop the feed to the cylinder and therefore the hot water.
If you need to drain down your central heating system to carry out repairs or maintenance, you need to know how to temporarily stop it refilling. On a sealed system there is no new water being supplied unless the filling loop is opened. On a vented system, the water level is kept topped up by the feed and expansion cistern. To drain down this type, temporarily close off the supply from here till you’re ready to refill. Either close off the valve on the incoming pipe to the cistern or, fix a batten across the top and tie up the float valve.