Turning off Your Water Supply Using The Water Main Supply Valve

What is a Water Main Supply Valve?

A Water main supply valve is essentially a tap to turn the water supply into your property on and off. 

There are usually 2 water main supply valves, one at the edge of your property boundary and another inside your property where the water supply pipe enters the building. 

If you do not know the location of your water mains supply valve, then you need to locate it as a matter of urgency. The water supply valve allows you to turn off all water to your property, which is perfect if, for instance, your house develops a leak. 

Water Mains Supply Valve With Cover Opened

How Do I Turn off My Main Water Supply?

To turn off your main water supply, the first thing you need to do is locate the internal or external stop cock. Once you have located either you can turn off the water supply into your property. 

If you have an external water leak then you will need to turn off the water supply at the boundary, if the leak is inside your home then the internal stock cock can be used. 

How Do I Find The Mains Water Shut Off Valve In The Street?

Typically it will be outside the boundary of your property. Look for an 8-inch iron or plastic cover which should have an M or a WM on it. Use a flathead screwdriver to lift the cover-up. Some of these will then have a frost cover which you need to remove to expose the stop cock.

Turn the stop cock clockwise to turn the water off and anti-clockwise to turn the water back on. This will be required for any water leak detection and repair processes.

Look Inside Your Property

If you are unable to locate the external water main supply valve or cannot turn it off, the next part of the process is to look inside your property to find the internal stopcock. While this will not resolve the water mains supply pipe issue, it will stop any more water coming into your property. 

An internal stopcock is usually located on the ground floor, on the inside a perimeter wall and possibly inside a cupboard or under the kitchen sink. The internal stopcock is normally a brass tap or a gate valve with a coloured handle. 

Check Your Home Buyers Report

Another important tip, particularly if you are preparing in case a leak ever occurs, is to check your home buyer’s report, as this may well help you to identify the location of the internal stopcock. It will also explain who is responsible for mains water leaks.

2 Main Types Of Mains Shut Off Valve

When it comes to working out how to detect a water pipe leak underground, one of the most important parts of the process is turning off the mains shut-off valve. There are typically two types of mains shut-off valves. Being able to identify the different types may help you in the case of a leak. 

The two different types are called:

Gate Valve On Incoming Water Main

Gate Valve

A gate valve is a type of valve that stops or permits water to flow with the use of a rectangular gate. When the valve opens, the gate or wedge is lifted, allowing the water to flow freely. When the wedge is lowered, the valve closes, stopping the water from flowing. 

Water Main Tap Valve Under Kitchen Cupboard

Tap Valve

A Tap Valve Stop Cock is much the same as a traditional tap. It has a handle at the top, which you twist to open or close the valve. 

Water Main Valve FAQs

Yes, this is a perfectly safe thing to do, and indeed if you are going on holiday, for instance, it might well be advisable as if any leak does develop whilst you are away, there will be minimal damage.

No, this is not necessary. Many people think that turning off the water will damage your boiler in the same way that boiling a kettle without water would. However, the chances of any damage being caused are minimal.

While replacing the mains water supply valve is possible, this is not a DIY task and is best left to a professional plumber. 

Adrian Morgan

Adrian Morgan CIPHE RP RHP is the founder & Managing Director of ADI Pro Leak Ltd. Adrian is also the Head Plumbing, Heating & Leak Detection engineer at ADI Leak Detection.

Adrian CIPHE RP RHP is proud to be registered with the Chartered Institute of Plumbing & Heating Engineering, a Registered Plumber and a Registered Heating Professional.