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What are the water valves in a house for?
The water valves in a house control where water can flow, from the main stop tap that shuts off the whole supply to small isolating valves that shut off a single tap, toilet or appliance. Knowing where they are makes leaks easier to deal with and repairs quicker for a plumber.
Last reviewed:Which water valves will you find at home?
Most homes have several kinds of valve on the cold and hot water pipes. They do different jobs, so it helps to know which is which before something leaks.
| Valve | Where it usually is | What it does |
|---|---|---|
| Internal stop tap (stopcock) | Where the supply comes in, often under the kitchen sink [S1] | Shuts off the cold water to the whole house |
| External stop tap | Under a small cover in the path, drive or pavement | Shuts off the supply before it reaches the house |
| Isolating or service valve | On the pipe just before a tap, toilet, washing machine or dishwasher | Shuts off one fitting so it can be worked on |
| Gate valve | Often on pipes from a cold water tank in the loft or airing cupboard | Shuts off flow from a tank |
| Float valve (ball valve) | Inside a toilet cistern or a cold water tank | Lets water in until the level is right, then closes |
| Pressure reducing valve | On the incoming main in some homes | Lowers high mains pressure for the house |
QuoteZila is starting in Cheshire, with Crewe, Nantwich and Sandbach among the first towns, and anyone in the UK can post a job. This page explains what the valves are for and when to call a plumber.
How do you find the stop tap?
WaterSafe, the national register of approved plumbers, says the internal stop tap is usually under the kitchen sink, and lists other common spots: under the stairs, in a garage or utility room, in a downstairs bathroom or toilet, in a kitchen cupboard or in a cellar [S1]. It may be called a stopcock or a stop valve. It usually looks like a tap with no spout, or a lever, sitting between two lengths of pipe.
Once you have found it, it is worth labelling it so anyone in the house can find it quickly. WaterSafe also suggests checking it works around every six months [S2]. A stop tap that has not been turned for years can seize, and you do not want to find that out during a leak.
If you live in a flat, the stop tap may be inside your flat, in a shared cupboard or somewhere only the building manager can reach. Ask the landlord or managing agent where it is before you need it.
What are isolating valves for?
An isolating valve, sometimes called a service valve, lets you shut off one fitting without turning off the whole house. You will often find them on the pipes under a basin, behind a toilet and on the hoses to a washing machine or dishwasher.
They come in two common forms:
- Slotted valves, with a small slot you turn a quarter turn with a flat screwdriver. When the slot runs along the pipe, water flows. Across the pipe, it is closed.
- Lever valves, with a small handle you turn a quarter turn. Many washing machine valves are like this.
If a tap is dripping or a toilet keeps running, a plumber will usually close the isolating valve to work on it. Where there are none, they may suggest fitting them at the same time, which makes later repairs quicker.
Why does a float valve matter?
The float valve, also called a ball valve or fill valve, is the part inside a toilet cistern or cold water tank that refills it. When the water reaches the right level, the float rises and closes the valve. If it sticks or the washer wears, water keeps running into the overflow.
Signs the float valve needs attention include:
- a toilet that keeps refilling or hissing
- water dripping from an overflow pipe on an outside wall
- a cistern that fills very slowly
- a loft tank that is overflowing or noisy
These are routine repairs, but an overflowing loft tank can soak a ceiling, so get it looked at quickly.
When should you call a plumber?
Call a plumber if:
- the stop tap is seized, leaks round the spindle or will not shut the water off
- there is no stop tap you can find or reach
- you want isolating valves fitted to taps, toilets or appliances
- a float valve or gate valve keeps leaking or will not close
- the water pressure has changed and you suspect a valve on the main
WaterSafe keeps a register of approved plumbers that you can search [S3]. If water is pouring through a ceiling and the stop tap will not move, tell the plumber that when you call so they can judge how urgent it is. The outside stop tap may belong to the water company, so your supplier can also advise.
Jobs you might post
These are examples, not taken from real job posts.
- "Kitchen stop tap is seized and will not turn. Would like it replaced and tested."
- "No isolating valves under the bathroom basin or behind the toilet. Please fit them while fixing a dripping tap."
- "Toilet cistern keeps refilling and the overflow outside drips. Need the fill valve looked at."
Get quotes from plumbers
Describe the valve, where it is and your postcode. Up to five matched local businesses can send you a quote [QZ2]. QuoteZila is free for customers and local businesses [QZ1].
Honest status: QuoteZila is new. We're starting in Cheshire, beginning with Crewe, Nantwich and Sandbach, and growing area by area. Anyone in the UK can still post a job or register a business. How fast you get quotes depends on how many local businesses have joined near you. Businesses can register and receive jobs straight away. We don't check insurance, qualifications or registrations, so please check these yourself before you hire.
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See our plumbers page and the plumber cost guide for how plumbing prices are built.
Questions about water valves
Where is the main water valve in a house?
WaterSafe says the internal stop tap is usually under the kitchen sink, but it can also be under the stairs, in a garage or utility room, in a downstairs bathroom or toilet, in a kitchen cupboard or in a cellar. There is often a second stop tap outside, under a small cover in the path or pavement.
Which way do you turn a water valve to shut it off?
Most round-handled stop taps close when turned clockwise, and it can take a few minutes for the flow to stop. Turn it slowly and do not force it. Small isolating valves with a slot are usually closed by turning the slot across the pipe with a flat screwdriver.
How often should I check my stop tap?
WaterSafe suggests checking that your stop tap works around every six months, so you know it will turn when you need it. If it is stiff, seized or will not shut the water off, ask a plumber to look at it rather than forcing it.
Can a plumber replace a stuck stop tap?
Yes. Replacing an internal stop tap, or fitting isolating valves where there are none, is ordinary plumbing work. WaterSafe lists approved plumbers you can search for. Ask whether the price includes shutting off the outside supply and testing afterwards.
Does QuoteZila check the businesses?
No. We don't check insurance, qualifications or registrations, so please check these yourself before you hire. You can report a quote or a business from your job page.
This page is general information, not professional or legal advice. QuoteZila does not check Gas Safe, WaterSafe, NFRC, NICEIC or other registrations against the register on your behalf: look them up yourself.
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Related pages
- Change a Tap Cartridge: What Is Involved. When a dripping mixer tap needs a new cartridge, how to identify the right part, what the job involves and when it is simpler to ask a local plumber to do it.
- Choosing a Drain Unblocker in Cheshire. How to choose a drain unblocker in Cheshire without naming a product. Match the fitting, read a biocide label, and see what a written quote should cover.
Sources
- QZ1: QuoteZila product fact. QuoteZila home and jobs-for-tradesmen copy.
- QZ2: QuoteZila product fact. QuoteZila FAQ and app README.
- S1: How can I locate my internal stop tap, WaterSafe. Accessed 2026-10-25. https://www.watersafe.org.uk/advice/weather-hacks/locate-internal-stop-tap/
- S2: Check your stop tap, WaterSafe. Accessed 2026-10-25. https://www.watersafe.org.uk/news/latest_news/stop_tap_check/
- S3: WaterSafe Register home page, WaterSafe. Accessed 2026-10-25. https://www.watersafe.org.uk/