How to Turn Off Water Supply – DIY Guide
To turn off your water supply, locate the main stopcock — usually under the kitchen sink or where the mains pipe enters the property — and turn it clockwise until it stops. For individual fittings, use the isolation valve on the supply pipe.
- Flat-head screwdriver
- Adjustable spanner
- Torch
- Bucket
- Old towels or rags
- Replacement isolation valve (if existing one is seized)
- PTFE tape
- Pipe repair clamp (emergency use)
Step-by-Step Guide
Locate Your Main Stopcock
The main stopcock is the single most important valve in your home — it controls all water entering the property. In most UK homes it sits under the kitchen sink, but it can also be found in an airing cupboard, under the stairs, or where the supply pipe comes through the external wall. If you have never found yours, do it now before you need it in an emergency. Our complete plumbing guide covers the full layout of a typical domestic plumbing system to help you understand where each component sits.
Turn Off the Main Stopcock
Turn the stopcock handle clockwise — the standard ‘righty-tighty’ rule applies. A quarter-turn lever valve will click into the closed position with the handle perpendicular to the pipe. A traditional brass wheel-head valve needs several full clockwise turns until it stops. Do not overtighten: stopping firmly when resistance increases is enough. Open a cold tap at the kitchen sink immediately afterwards to confirm the supply is off and to release pressure from the downstream pipework.
Use an Isolation Valve for Individual Appliances
Most modern plumbing includes inline isolation valves — small brass or plastic valves with a flat-head slot — on the supply pipes feeding individual taps, toilets, and appliances. Turning the slot a quarter-turn so it sits across the pipe (perpendicular) closes it. This lets you isolate a single fitting, such as a toilet cistern or washing machine, without cutting water to the whole house. This is the correct approach when you want to replace a kitchen tap or service a specific appliance.
Drain Down the Affected Pipework
Even after closing the stopcock or isolation valve, water remains in the pipes. Open the lowest tap in the house — usually a downstairs cold tap — and let it run until flow stops. For hot-water work, also open a hot tap at the lowest point. This prevents water spilling when you disconnect fittings and reduces the risk of scalding if hot pipework is involved. Place a bucket and old towels under any joint you plan to open, as residual water will still drain out when the pipe is cut or disconnected.
Handle a Seized or Stuck Stopcock
Stopcocks that have not been operated for years often seize. Apply penetrating oil around the gland nut and spindle, wait ten minutes, then try again with gentle pressure using an adjustable spanner on the body of the valve — never force the handle alone or you may snap it. If the stopcock fails entirely, you will need to shut off water at the external boundary stopcock, which is located inside a small covered chamber (buffalo box) near the pavement. Use a long-handled stopcock key to reach it. If the external stopcock is also faulty, contact your water company — they are responsible for it. For related repair work, see how to fix a dripping tap once the water is safely isolated.
Restore the Water Supply and Check for Leaks
When your repair or job is complete, close all open taps first, then open the stopcock or isolation valve slowly — turning it anti-clockwise — to restore flow. Bringing pressure back gradually reduces the risk of water hammer and joint stress. Check every fitting you worked on for drips, and inspect nearby joints for at least five minutes before considering the job done. If you have replaced any tap components, this is also a good time to check the flow; if pressure seems low afterwards, see our guide on replacing a tap washer as a worn washer can restrict flow once pressure returns.
Frequently Asked Questions
Where is the stopcock in my house?
In most UK homes the internal stopcock is under the kitchen sink, where the cold mains supply enters the property. If it is not there, check the airing cupboard, under the stairs, or at floor level near the front external wall.
What do I do if my stopcock will not turn?
Apply penetrating oil to the spindle and gland nut, wait ten minutes, and try again using an adjustable spanner for leverage on the valve body — never the handle alone. If it still will not move, shut off at the external boundary stopcock using a stopcock key and call a WaterSafe-registered plumber to replace the internal valve.
Where is the external stopcock and who is responsible for it?
The external stopcock sits in a small covered chamber (buffalo box) set into the pavement or driveway near your property boundary. Your water company owns and is responsible for it; you are responsible for everything on your side of it. You can use a long-handled stopcock key to operate it yourself in an emergency.
Can I turn off water to just one tap or toilet without shutting off the whole house?
Yes — most modern plumbing has inline isolation valves fitted directly on the supply pipes feeding individual fittings. Turn the flat-head slot a quarter-turn so it sits across (perpendicular to) the pipe to close it. If there is no isolation valve, you will need to use the main stopcock. Fixing a running toilet is a typical job where an isolation valve lets you work without cutting the whole house supply.
Is turning off the water supply something I need a plumber for?
Operating a stopcock or isolation valve is a straightforward task any homeowner can do — no qualifications are required. However, if you need to repair or replace pipework, fittings, or gas-adjacent components, always check whether the work requires a WaterSafe-registered plumber or whether it involves any notifiable work under Building Regulations. The HSE and gov.uk both set out when professional sign-off is needed for domestic plumbing.
Before working on any plumbing, operate your stopcock fully open and then back a quarter-turn from fully open — this prevents the valve seizing in the open position over years of non-use, and means it will actually close when you need it in an emergency. Most seized stopcocks fail simply because they were never exercised.
Sources
- WaterSafe — How to find and use your stopcock — watersafe.org.uk
- Thames Water — How to turn off your water supply — thameswater.co.uk
- HSE — Water supply and plumbing: domestic guidance — hse.gov.uk
Safety Notice: Electrical and plumbing work can be dangerous if done incorrectly. In the UK, certain electrical work must comply with Part P of the Building Regulations and certain plumbing work with Part G. If in doubt, consult a qualified electrician (NICEIC/NAPIT registered) or plumber (CIPHE/WaterSafe registered). This guide is for general information only — it is not a substitute for professional advice.
