How to Turn Off Your Water Supply

Do this now

1. Find the inside stop valve and turn it clockwise. Thames Water describe it as usually sitting just after the water pipe enters the house, most often under the kitchen sink. It takes several turns, not a quarter turn. If you cannot see it, where is my stopcock lists the places it hides in London properties.
2. Open the cold tap over the kitchen sink. That drains the standing water out of the rising main rather than leaving it to keep feeding the leak. Thames Water warn that taps can run for a few minutes after the valve is shut for exactly this reason.
3. Open the other cold taps, lowest floor first. On a leak that is running through a ceiling, this is the fastest way to empty the pipework above it.
4. Switch off anything that heats water. Immersion heater at the switch, and the boiler at its own switch. Both can be damaged by running dry.
5. If the water does not stop, use the outside stop valve. Thames Water keep this one for emergencies, such as a leak on the supply pipe between the outside and inside valves, and it usually needs a stop tap key. Turn it clockwise, and never force it.

Then deal with the water already out: keep people away from a bulging ceiling, and turn off the electrics to any affected circuit at the consumer unit rather than touching wet fittings.

What the stopcock does not turn off

This catches people out, because the tap keeps running and they assume the valve failed.

What you have	What closing the stopcock does
Mains-fed cold taps and a combi boiler	Stops everything within a minute or two
A cold water storage tank in the loft	Stops the refill, but the tank keeps feeding whatever it serves until it empties. Sometimes that is a long time and a lot of water
A hot water cylinder	The cylinder stays full and can keep draining through the hot taps
A sealed heating system	Nothing. The heating circuit is closed and holds its own water, which is why a radiator or underfloor leak does not stop when the mains does
A leak in the flat above	Nothing. Their supply, their valve

If the water keeps coming after the mains is off, that is useful information rather than a failed attempt: it tells you the leak is on the heating circuit, on the stored water side, or not in your property at all.

Isolate one thing instead of the whole house

Most leaks do not need the house shut down. There is usually a smaller valve closer to the problem.

• Service valves on the pipes feeding basins, toilets and taps, usually a slotted screw in the body of the valve. A quarter turn with a flat screwdriver, so the slot sits across the pipe, closes it.
• Washing machine and dishwasher valves behind or beside the appliance, normally a small lever.
• The toilet fill valve, which is the one people turn the whole house off for when a cistern will not stop filling.
• Radiator valves at each end of a leaking radiator, which isolate it from the rest of the heating without draining the system.

Shutting a branch rather than the main means you keep drinking water and a working toilet while the repair is arranged, which matters if the work is going to take more than an afternoon.

Turning off the water to one radiator

A radiator is on the heating circuit, not the mains, so the stopcock does nothing to it. It has its own two valves, one at each end, and closing both cuts it off from the rest of the system.

1. Heating off first, and let the radiator cool.
2. Close the control valve. On a thermostatic valve, turn the head to its lowest or off setting. Some only close fully with the head removed and the plastic cap that came with it screwed on in its place. On a manual valve, turn it clockwise until it stops.
3. Close the lockshield at the other end. Pull off its plastic cover and turn the spindle clockwise with a spanner or pliers. Count the turns as you go, because that is how you set it back to the same balance afterwards.
4. Check it has held. Put kitchen roll under the leak. If it is still wet after half an hour, one of the valves is not sealing, or the leak is on the pipe below the valve, which the valves cannot isolate.

If the leak is at the valve itself, the detail on what each kind of weep means is on a radiator leaking from the valve.

In a flat: when there is no stopcock you can find

Many London conversions and purpose-built blocks have the flat's stop valve somewhere unexpected: in a cupboard on the landing, in a riser behind a panel, in the ceiling void of the flat below, or in a communal plant room. Check these before you assume you do not have one:

• The kitchen, under the sink and behind the kickboards.
• The airing cupboard or wherever the cylinder or boiler is.
• A service cupboard in the communal hallway, often marked with your flat number.
• Behind a bath panel or in boxing at low level in the bathroom.

If you still cannot find it, call the managing agent's out-of-hours line. They hold the building plans and usually know where each flat's isolation is. Do not close a communal valve without telling them, because it may cut off other flats too. For the places it hides in more detail, read where is my stopcock and how to turn it off.

If the valve is seized, or you are afraid to force it

Old brass stopcocks that have not been moved in twenty years often will not move, and the ones that do move sometimes weep from the gland afterwards. Thames Water's advice on the outside valve is blunt about never applying excessive force, and the same applies indoors: a snapped spindle on a live main turns a small job into a very wet one.

Options, in order: work the handle gently back and forth rather than hauling on it, try penetrating oil on the spindle, or leave it and use the outside valve instead. Thames Water also point at permanent fixes where the inside valve is unusable, including a SureStop or Aladdin type valve, and mention freeze-clamping by a plumber as a temporary measure. If yours starts dripping from under the handle once you have turned it, that is the gland packing, and it is covered on stopcock leaking.

Turning it back on

Slowly, anti-clockwise, with one cold tap open so air can escape. Then walk the property and look at everything the mains pressure has just hit again: under the sink, behind the washing machine, at the stopcock itself, and at any joint that was disturbed. A system that has been off and drained sometimes reveals a second weep when it is repressurised, particularly on old compression joints.

Once the water is on and stable, read your meter with everything off, wait half an hour, and read it again. If the numbers have moved, something is still running. That test, and what to do with the result, is on the water meter turning with everything off.

When turning it off is only buying time

The symptom that means the shut-off is masking a leak rather than solving one: you close the stopcock, the flow stops, you open it again hours later and water appears within minutes at the same spot, with no visible fitting to blame. Nothing has been fixed. The mains was simply feeding a hole somewhere you cannot see, and it started feeding it again.

The same applies to the ceiling that dried out and then marked again after the water came back on, and to the patch of floor that is warm or damp whenever the supply is live. Those are pipes inside the structure, and they are found with acoustic listening, thermal imaging and tracer gas rather than by opening things up to look.

That work is charged at our hourly rate, fixed before we attend, and if we do not find the leak you do not pay for the time we spent looking. Water leak repair covers the trace and the repair together, and if the leak turns out to be outside on the supply pipe, mains and supply pipe repair is the relevant one.

If you are turning the water off to deal with a dripping tap, how to change a tap washer walks through the rest of the job.