What's a stopcock and what does it do?

Ben Cooper
Written by: Ben Cooper
Posted on: 6 April 2016

Not sure what a stopcock is? Join the club. Take a look at our stopcock video, Stopcocks Uncovered, to find out all you need to know:


Still confused? Read our article and become a stopcock connoisseur.

Your stopcock is the control tap for your mains water. If you’re unfortunate enough to have a burst pipe or broken tap, with water pouring everywhere causing damage to your floors and furnishings, then you need to find your stopcock sharpish. If you don’t, your home could be badly damaged before the plumber arrives.

Generally speaking most homes have an internal stopcock and an external stopcock.

The external valve controls the flow from the water main that serves your street to the supply pipe into your house.

If your supply pipe leaks or ruptures then the external stopcock will need shutting off to allow for repairs and to stop masses of water saturating the floor.

Your internal stopcock turns off the water from the supply pipe as it enters your property, and can be located in a variety of places (we’ll go into that later).

In fact, some people find their stopcock in some truly bizarre locations, as they often get moved or built around as houses get remodelled or renovated. This is why many people don’t know where their stopcock is.

So now you know what a stopcock is, the next step is to find it.

What does a stopcock look like?

A stopcock looks like a tap, but without an outlet spout. It will be situated between two lengths of pipe, acting as a connector. This allows the stopcock to impede the flow of water when it is closed off.



Where is my stopcock?

This is the million-dollar question for many people, as they simply don’t know where their stopcock is.

“Where’s my stopcock?” isn’t a question you want to ask a plumber down the phone when you have a burst pipe emptying gallons of water into your home.

You need to know where it is so you can shut off the water quickly and limit the damage before a professional has a proper look at the problem.

Remember, you probably have two stopcocks: one inside the property and one outside.

Your external water mains stopcock will most likely be located on the street, just outside the boundary of your property. Some properties will have the mains stopcock within the boundaries, often in the front or back garden areas.

In either case it should be marked clearly by a metal cover, usually with the word ‘water’, ‘stopcock’ or a simple ‘W’ stamped on the surface.

Internal stopcocks can be much harder to locate, especially in older properties. Here is a list of the most common places to find a water stopcock:

  • Under the kitchen sink
  • In the bathroom
  • Cupboard under the stairs
  • By the gas meter
  • In a utility room
  • In a cellar
  • In a cupboard – this can be common for flats and they can sometimes be in communal corridors where you will find stopcocks for other flats

If you can’t locate your stopcock it can be worth asking your neighbour where theirs is, especially if you live in older terraced houses or flats, as they will often be in similar places. In old properties it may be located under the floorboards near the front door, which is inconvenient to say the least.

When you do find it, make sure to test if it’s working. Stopcocks can seize up if left in one position for a long time and you don’t want to be unable to shut it off in an emergency.

Quite often they can be loosened with some WD40 or similar lubricant. Just be careful not to force the valve too hard. If you’re in doubt then get a plumber out to see to it.

Know where your stopcock is so you can shut off the water quickly and limit the damage before a professional has a proper look at the problem

How to turn water off

In the event of a leak or a burst pipe, you need to know how to turn the water off. This isn’t a difficult job at all, as long as your stopcock is in good working order.

To turn off your external stopcock you will most likely need a stopcock key. This is a long metal tool that has a T-bar handle at one end and a special fitting at the other that fits around the stopcock valve.

Insert the stopcock key down into the shaft and slip the end onto the valve. Then turn the key clockwise until the water flow stops. Mains stopcocks can be stiff so it may require a bit of force to get it turning.

If the T-bar handle is across the pipe it should be shut, if it is inline with the pipe then the mains should be open.

Turning off the water with your internal stopcock can often be done by hand, but you may need a set of pliers to fully close it or get it moving if it’s stiff. It’s the same procedure as the external stopcock: turn the handle clockwise until the water stops. When you are ready to turn it on again turn it back anticlockwise.

Knowing where your stopcock is, and how to turn it on and off, could save your home from extensive damage if you get a serious leak. It’s also important to know about it if you’re going to undertake any DIY plumbing work like changing a worn washer on a tap.

If you have a leak then turn off the water as fast as possible and call in an emergency plumber to fix the problem.

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