How to find and turn off your stopcock

The stopcock, also called a stop tap or stop valve, controls the mains cold water coming into your home. If a pipe bursts, turning it off is the quickest way to stop the water.

Find it on a calm day rather than in the middle of a leak. Check that it turns, clear anything stored in front of it, and make sure everyone at home knows where it is.

The stopcock is usually close to where the supply pipe comes into the building, normally at the front. The most common places are:

• Under the kitchen sink, the most likely spot in most homes
• Under the stairs, or in a downstairs cloakroom or utility room
• Under a floorboard or small hatch in the hallway near the front door, which is common in Victorian and Edwardian terraces
• In the cellar or basement, where the supply pipe comes through the front wall
• In a garage, or in the airing cupboard next to the hot water cylinder

Each flat should have its own stopcock, but in converted houses and older blocks it isn't always inside the flat. Start under the kitchen sink, then check the airing cupboard, behind the bath panel, beside the boiler or hot water cylinder, and in any cupboard near the front door.

If it isn't inside, it may be in a communal riser cupboard on the landing, in a basement plant room, or in a row of valves serving the whole building. The managing agent, freeholder or caretaker should know which valve is yours and may hold the key to the cupboard.

In a basement flat, the supply usually comes in at the front, so check under the front windows, under the steps down from the street, and in any vault or cupboard at the front of the flat.

Some newer homes have a push-button or switch-style stop valve instead of a handle, often near the kitchen sink. If yours does, follow the instructions printed on it. For a traditional stopcock:

1. 1Turn the handle clockwise until it stops. On a lever-type valve, turn the lever a quarter turn so it sits across the pipe rather than along it.
2. 2Turn on the cold kitchen tap. The flow should slow and stop within a minute or so as the pipes empty.
3. 3If water still runs steadily, the stopcock may not be closing fully, or the tap may be fed from somewhere else. Look for a second valve, or use the outside stop tap described below.
4. 4Leave the water off until the leak has been repaired. To turn it back on, open the stopcock anticlockwise slowly, a little at a time, and check for leaks as the pipes refill.

Stopcocks that haven't been touched for years often seize. Don't force one with a wrench, a hammer or a length of pipe for extra leverage. Old stopcocks can snap or start leaking around the spindle, which leaves you with a bigger problem and no way of turning the water off.

Try gently working the handle a little in each direction. If it still won't move, or it starts to drip around the spindle, leave it and use the outside stop tap instead, then have it replaced. A plumber can fit a new stopcock or isolation valves so each part of the system can be shut off on its own.

Most homes also have an outside stop tap, usually under a small metal or plastic cover in the pavement or front garden, near the boundary. The cover is often marked 'W' or 'Water'. It's part of your water company's network rather than your own plumbing, and it usually needs a long stop tap key to reach.

In older London streets, one outside stop tap sometimes supplies more than one property. If you can't stop a leak from inside, contact your water company: your water bill shows which one supplies you.

1. 1With the stopcock off, open the cold taps to drain the water left in the pipes.
2. 2Switch off the boiler, and the immersion heater if you have one.
3. 3If water is near lights, sockets or the consumer unit, switch off the electricity at the consumer unit, but only if you can reach it safely while standing somewhere dry. Keep out of any room where the ceiling is bulging.
4. 4If your home has a cold water tank in the loft, water can keep flowing from it after the stopcock is off. Close the valve on the pipe leaving the tank if there is one, or run the bath taps to empty it.
5. 5Catch what you can with buckets and towels, take photos for your insurer, and call a plumber.

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