Knowing how to shut off the water supply to your home before a problem occurs is one of the most practically useful pieces of household knowledge. When a pipe bursts or an appliance fails, the difference between a minor flood and serious structural water damage can be a matter of minutes spent locating the stopcock.

The Internal Stopcock

Most UK homes have an internal stopcock that controls the flow of cold mains water into the property. Turning this stopcock off stops water flowing into the house, allowing you to deal with a leak or plumbing emergency without the situation worsening.

The most common location for an internal stopcock in a UK house is under the kitchen sink. It is typically a brass valve on the cold water supply pipe, with a flat-head screw slot or a lever handle. To close it, turn it clockwise, a full quarter-turn for a lever valve or multiple turns for a screwtype valve, until it is fully closed. A tag of some kind on the stopcock as a reminder of its location is worth putting in place once you have found it.

Other common locations include under the stairs, in a downstairs toilet, in a utility room, or in a ground-floor cupboard. Some older properties have the stopcock in the cellar or at the point where the supply pipe enters the building through the floor. If you cannot find it in the obvious locations, trace the cold supply pipe from under the kitchen sink back toward where it enters the property.

The External Stop Valve

In addition to the internal stopcock, there is an external stop valve, or external stopcock, in the pavement or verge outside the property. This is a valve in a small underground chamber, typically covered by a metal or plastic cover at ground level. Turning this off stops all water supply to the property from the street main. You may need a long-handled stop valve key to reach and turn it, which can be bought from a plumbers merchant or DIY store for a few pounds.

The external stop valve is useful if the internal stopcock is inaccessible, seized, or has failed. In a serious flooding emergency, turning off both the internal and external valves gives maximum protection.

What to Do After Shutting Off the Water

Once the water supply is off, turn on a cold tap to release pressure remaining in the pipes and confirm that supply has stopped. If the emergency involves a burst pipe, electricity near the leak should be turned off at the consumer unit if there is any risk of water reaching electrical fittings. Call a plumber for emergency repairs; many operate 24-hour emergency callout services.

Hot Water Supply

Shutting off the mains cold water supply also stops cold water feeding the hot water cylinder or combination boiler. For properties with a hot water storage cylinder in the loft, there is often a separate gate valve on the supply to the cylinder. Turning this off isolates the hot water without affecting the cold water supply to the rest of the house.

Summary

The internal stopcock, most commonly found under the kitchen sink, is the primary way to shut off the water supply to a UK home. Turning it fully clockwise closes the supply. An external stop valve in the pavement outside provides a backup if the internal valve fails. Testing the stopcock annually ensures it works when needed. Knowing where the stopcock is before an emergency occurs is one of the most practical pieces of preparation any homeowner can make.