What Is a Stop Valve and How Does It Work? - 2026

It's a Sunday morning, you're enjoying a cuppa, and suddenly you hear it. That unmistakable sound of water gushing where it shouldn't be. Your first thought? "Where's that valve to turn the water off?" Knowing where your stop valve is and how it works can be the difference between a minor inconvenience and a full-blown flooding disaster.

Quick Take: A stop valve (also called a stopcock) is your home's main water shut-off control, typically found under the kitchen sink or near where water enters your property. It stops water flow when turned clockwise, preventing leaks and allowing safe repairs. In Surrey homes, you'll usually find two: one inside your property and one outside at the boundary.

What Is a Stop Valve (Stopcock) and What Does It Do?

A stop valve is essentially your home's water on/off switch. It's a valve fitted to your incoming water pipe that can completely shut off the flow of water into your property.

When you turn your stop valve off, you're stopping water from entering your home. This becomes crucial during plumbing emergencies like burst pipes or major leaks. Without a working stopcock, a small leak can quickly turn into serious water damage.

Stop valves are typically located near where the water supply enters your property. In most Surrey homes, you'll find one by your water meter or main entry point. Turn it one way, water flows. Turn it the other, water stops.

Stop Valve vs Stopcock: Are They the Same Thing?

Yes, they're exactly the same thing. Stop valve and stopcock are just different names for the identical device. You'll hear both terms used interchangeably, especially here in the UK where "stopcock" is the more traditional term.

Some people also call it a shut-off valve or main water valve. There's no functional difference between these terms. However, there are different types of stop valves - older traditional stopcocks with wheel-like handles that need multiple turns, or modern ball valves with levers that only need a quarter turn.

Where to Find Your Stop Valve in Surrey Homes

Finding your stop valve before you actually need it is one of the smartest things you can do as a homeowner. Trust us, you don't want to be hunting for it whilst water's pouring through your ceiling.

In most Surrey properties, you'll have two stop valves:

Internal Stopcock

Your internal stopcock is usually located where the water pipe enters your home. The most common spot? Under the kitchen sink. Have a look in the cupboard beneath your sink and you'll likely spot it attached to the pipe coming up from the floor or through the wall.

If it's not there, check these other typical locations in Guildford, Woking, and across Surrey:

• Ground-floor bathroom (often under the sink or near the toilet)

• Utility room or downstairs loo

• Under the stairs in a cupboard

• Near your front door (older properties sometimes have them here)

• Under floorboards near the entrance (more common in Victorian or Edwardian homes)

The valve itself looks like a tap without a spout, sitting in-line on a pipe. It'll have either a traditional cross-head handle or a more modern lever.

External Stopcock

Your external stop valve sits at your property boundary, usually in a small covered pit or metal box. Look for a small rectangular or circular cover in your front garden, driveway, or pavement marked with "Water" or just "W."

This outside valve connects directly to the street main and typically requires a special stopcock key to operate. Be aware that in some cases, particularly in Sutton and Epsom terraced properties, this external valve might be shared between multiple homes.

Top tip: Once you've found your stop valve, take a photo of its location and test it works. You'll thank yourself later.

How to Turn Off Your Water Safely (Step-by-Step)

Knowing how to shut off your water properly can save you from disaster. Here's how to do it safely:

Step 1: Notify and Prepare

Let everyone in your home know you're turning off the water. If you've got a water heater or boiler, turn it off first. Electric heating elements can burn out if they're heating an empty tank.

Step 2: Locate Your Main Stop Valve

Head to your internal stopcock. It'll have either a lever handle or a round wheel-like handle on the incoming water pipe.

Step 3: Turn It Off

Here's where "righty-tighty, lefty-loosey" comes in handy:

• For wheel/cross-head handles: Turn clockwise (to the right) until it won't turn any more

• For lever handles: Turn the lever a quarter-turn so it sits perpendicular to the pipe

Don't force it. If it's stuck (a common problem we see across Reigate and Camberley), you risk snapping the valve.

Step 4: Drain the System

Once the main valve's closed, open faucets at the lowest and highest points of your home. This lets water drain from the pipes and relieves pressure in the system.

Step 5: Restore Water Carefully

When you're ready to turn the water back on, close all open taps except one (to let air escape). Then slowly turn the stopcock anti-clockwise. Going slowly prevents water hammer, that banging noise caused by sudden pressure surges.

Common Stop Valve Problems (Stuck, Leaking, Won't Fully Shut Off)

Stop valves can sit untouched for years, which means problems often surface right when you need them most. Here are the issues we see most often in Farnham and across Surrey:

Stiff or Stuck Stopcock

This is by far the most common problem. You go to turn your stopcock and it simply won't budge. Don't force it, or you'll snap it clean off.

What to do:

• Spray penetrating oil around the valve stem

• Let it soak for 10-15 minutes

• Gently try to work the handle back and forth

• Tap the valve body lightly with a hammer to help the oil penetrate

• Slightly loosen the small packing nut just below the handle

Once you've freed it, turn it open and closed a few times to clear debris. If these tricks don't work, it's time to call us at Plumbing Surrey.

Leaking Stop Valve

Noticed water dripping from your stopcock? First, work out where it's coming from:

Leak around the handle: Try tightening the small packing gland nut slightly. You can also wrap PTFE tape under the gland nut and then retighten it.

Leak at a joint: Carefully tighten the compression fitting.

Leak from the valve body: If the valve body's cracked or the leak won't stop despite tightening, you'll need a replacement.

Won't Fully Shut Off Water

You've closed the stopcock, but water's still trickling from your taps. This means the valve isn't sealing properly, usually due to a worn washer or valve seat inside.

If you're handy, you can try rewashering the stop valve yourself. However, if the internal mechanism's corroded, replacement is your best bet.

Prevention tip: Exercise your stop valves a couple of times a year. Just turn them off and on to keep them from seizing up.

Repair vs Replace: When You Need a New Stop Valve (and What Type to Choose)

So your stopcock's playing up. Should you fix it or fit a new one? It depends on the valve's condition and what's actually wrong.

When Repair Makes Sense

Minor issues are often fixable:

• Slight leak around the spindle: Tighten or repack the gland

• Stiff valve: Lubricate and work it free

• Worn washer: Replace the internal washer

If your stop valve is relatively modern and in decent overall shape, you don't necessarily need a new one.

When Replacement Is the Smart Choice

Consider replacing if:

• Your valve is decades old or visibly corroded

• It's an old-style gate valve (notorious for seizing)

• It won't fully close even after changing the washer

• You need excessive force to operate it

The main shutoff is far too important to leave unreliable.

Upgrade to a Better Valve

When replacing, seriously consider upgrading to a modern ball valve type stopcock. Traditional stopcocks in older Surrey properties often use a compression washer or gate mechanism. These can wear out, jam, or corrode over time.

A ball valve, by contrast, has a simple quarter-turn lever and a spherical shutter inside. It's incredibly durable and easy to operate. The cost difference is minimal (we're talking tens of pounds, not hundreds), but the reliability payoff is huge.

Final Thoughts on Stop Valves

Your stop valve might be small, but it plays a crucial role in protecting your home. Every homeowner in Dorking, Redhill, and right across Surrey should know exactly where their stopcock is. Take a few minutes right now to find and test it.

At Plumbing Surrey, we're always here to help keep life flowing smoothly. For more information, visit our about page or get in touch through our contact page.

Stop Valves FAQs

Are a stop valve and a stopcock the same thing?

Yes, absolutely. Stop valve and stopcock refer to the same mechanism. "Stopcock" is the term more commonly used in the UK, whilst "shut-off valve" might be heard in other countries. There's no functional difference at all.

Where is my stopcock likely to be located in my house?

Look near where the water supply enters your home. In most Surrey properties, the internal stopcock is found under the kitchen sink. If it's not there, check ground-floor bathrooms, utility rooms, under-stair cupboards, or by your water meter. Your external stop valve will be at the property boundary in a covered pit marked "Water" or "W."

How do I turn a stopcock on or off?

Most stop valves turn off by turning the handle clockwise (to the right) until it stops. To turn the water on, turn it anti-clockwise (to the left). For a lever-type valve, turning the lever perpendicular to the pipe means off, and parallel means on. Always turn slowly and gently.

What if my stopcock is stuck and I can't turn it?

Don't apply extreme force or you could snap it off. First, spray penetrating oil around the valve stem and give it 10-15 minutes. Then try to gently work the handle back and forth. You can tap the valve body lightly with a hammer. If you still can't shift it, call a plumber.

Who is responsible for the external stop valve outside my property?

In the UK, your water utility company is usually responsible for the external stopcock if it's in the public pavement or street. Generally, any stop valve within your property boundary is your responsibility as the homeowner, whilst those outside belong to the water company.