How to Turn Off Your Water Supply in an Emergency

Knowing how to turn off your water supply before an emergency happens is one of the most important things a London homeowner or renter can do. When a pipe bursts or a major leak starts, every second you spend searching for the stopcock means more water damage to your property.

Read this guide now, before you need it. Find your stopcock today and test that it works.

Step 1: Find Your Internal Stopcock

The internal stopcock (also called a stop valve) is the main valve that cuts the water supply to your property. In London homes it is most commonly located:

• Under the kitchen sink — the most common location in London houses
• In a downstairs cupboard near the front door
• Under the stairs
• In the bathroom or airing cupboard — common in flats
• In the utility room or garage
• Behind a small panel near the front door — very common in London mansion flats and Victorian conversions

Action now: Go and find yours. Make sure everyone in the household knows where it is.

Step 2: Turn Off the Stopcock

A stopcock looks like a tap handle or an oval-shaped valve. To close it:

• Tap-style stopcock: Turn clockwise (right) to close. "Righty tighty, lefty loosey."
• Oval/flat-head stopcock: Use a flat-head screwdriver or your fingers to turn it 90 degrees so the slot is perpendicular to the pipe — this closes it.

Once closed, open a cold tap in the kitchen to drain any remaining water from the pipes.

What If My Stopcock Is Stuck?

Stopcocks that haven't been turned in years can seize up. Do not force it with a spanner or wrench — this can shear the spindle, making it impossible to turn. Instead:

1. Apply penetrating oil (WD-40) around the spindle and wait 10 minutes
2. Try again gently — use a cloth for grip if needed
3. If it still won't move, use the external stopcock (see below)

After the emergency: Get a plumber to replace the faulty stopcock — a stuck stopcock is a serious liability. Replacement is a minor job costing around £50–£100.

Using the External Stopcock

If you can't find or use the internal stopcock, there is an external stopcock in the pavement outside your property, usually covered by a small metal plate marked "W" or with a water symbol. To use it:

• You need a special stopcock key (a long-handled T-bar tool, available from DIY shops for around £5–£10)
• Insert it into the access point and turn clockwise to close
• Note: the external stopcock may also supply neighbouring properties — don't use it unless necessary, and restore it promptly

Isolation Valves — Shutting Off Individual Appliances

You don't always need to turn off the whole supply. Isolation valves let you cut water to a single appliance or fitting:

• Under taps: Most modern London kitchens and bathrooms have isolation valves under the sink/basin — turn the screw slot to perpendicular to close
• Behind the toilet: An isolation valve on the supply pipe to the cistern
• Under the boiler: An isolation valve on the cold water feed to the boiler
• On the washing machine: Valves on both hot and cold feed hoses at the wall

Turning Off Water in a London Flat

Flats present additional complexity. In addition to your own stopcock, there may be:

• A building stopcock in a communal riser cupboard or meter room — managed by the building management company
• An individual flat isolation valve in a communal cupboard outside your front door
• A Thames Water external stopcock in the pavement outside the building

If a leak in your flat is affecting the flat below, act fast and use building management's emergency number if your own stopcock doesn't stop the flow.

After Turning Off the Water — What Next?

1. Call an emergency plumber — don't wait for the leak to "dry out." Water in walls and floors causes serious damage even after the supply is stopped. See: What to do when you have a leaking pipe
2. Document the damage — take photos and video immediately for your insurance claim
3. Contact your insurer — most home insurance policies cover water damage from sudden leaks
4. Move valuables and electronics away from the wet area
5. Switch off electricity in flooded areas at the fuse box

See also: 10 signs you need an emergency plumber right now

Frequently Asked Questions

Do I need a plumber to replace a broken stopcock?

Yes — replacing a stopcock requires turning off the water at the external supply point (Thames Water territory) and is a plumbing job. It's a minor repair that typically takes less than an hour and costs £50–£120 in London.

Should I test my stopcock regularly?

Yes — turn it off and back on once a year to prevent it seizing. While the water is off, check under sinks and around appliances for any small drips you may not have noticed.