Stopcock: What It Is, Where to Find It, and What to Do If It's Stuck

A stopcock is a valve fitted into your mains water pipe that lets you shut off the water supply to your property, or to part of it, by turning the handle clockwise. It's the single most useful thing to know the location of in any home, because it's the first thing you need during a burst pipe, a leaking tap, or before starting any plumbing repair.

• The internal stopcock is inside your property, usually a small brass or plastic tap-style valve
• The outside stopcock belongs to the water company and sits under a small cover near the property boundary
• Turning it clockwise closes it; anticlockwise reopens the supply
• Some larger London properties and blocks of flats have more than one, feeding different risers or units

The most common location across London housing stock is under the kitchen sink, facing the pipework where the mains water enters the property — start there first. London's mix of building types means the exact spot varies more than most guides admit.

• Victorian and Edwardian terraces (common across Tower Hamlets, Hackney and Newham) — often under the kitchen sink, but sometimes in a hallway cupboard, under the stairs, or beneath a floorboard near the front door
• Converted flats and period conversions — frequently in a hallway or utility cupboard, since original pipework has often been rerouted during conversion work
• New-build flats (common in Canary Wharf, Shoreditch and along the river) — usually in a labelled utility cupboard or service riser cupboard near the front door
• Outside stopcock — under a small metal or plastic cover in the pavement or front garden, usually near the boundary of the property

If you genuinely can't find one anywhere and need to isolate your water supply right now, see our guide to turning off your water supply for the outside stopcock and mains isolation options too.

A stopcock that won't turn has almost always seized from years of standing unused — the internal washer perishes, the spindle corrodes, or mineral deposits build up inside the valve body, all of which make the handle stiff or completely immovable. It's more common in older brass valves and in hard-water areas, and it's rarely a sign of anything wrong with the plumbing beyond the valve itself.

The mistake to avoid is forcing a stiff stopcock with pliers, a wrench, or serious hand strength — that's exactly what snaps the handle off or cracks the valve body, turning a five-minute job into a proper repair. Steady, moderate pressure is fine; if it doesn't move with that, stop.

Here's the safe sequence for locating and testing your stopcock without risking damage to the valve.

1. Locate the stopcock. Check under the kitchen sink first, then hallway or under-stairs cupboards, utility cupboards, or near the front door if it isn't there.
2. Clear access to the valve. Move any stored items blocking the pipework so you can see and reach the handle properly.
3. Turn the handle clockwise. Turn it firmly but gently with steady hand pressure — most stopcocks turn a quarter to a full turn to shut off fully.
4. Confirm the water is off. Run a tap; if it slows to a trickle and stops, the stopcock is working and fully closed.
5. If it won't move, stop and get help. Don't force it with pliers or a wrench — a stiff or seized stopcock that won't turn safely needs a plumber to free or replace it.

If you've followed this and the water's still flowing, or the stopcock is too stiff to move safely, that's the point to call rather than keep forcing it.

Call a plumber if your stopcock won't turn at all, is dripping from the spindle when you move it, or the handle has already snapped off — these need a proper repair or replacement, not more force. It's also worth calling if you can't locate a working stopcock anywhere in the property, since that leaves you with no way to isolate the water supply in an emergency.

RenoPlumb replaces internal and outside stopcocks and isolation valves across London from our E1 base, covering Tower Hamlets, Hackney, Islington, Newham and Southwark. See our stopcock replacement page for what that involves, or if water is actively leaking and you can't isolate it at all, treat it as urgent and see our emergency plumber page instead.

Call 07460 824073 and we'll talk you through what to do while we're on the way.

Cost depends on whether your stopcock needs freeing, a straightforward internal valve swap, or a more involved outside stopcock replacement that may need excavation — so we don't quote a figure until we've seen the job. Every job starts with a free, no-obligation quote before any work begins. See our pricing page for more on how we work out costs.

Need this fixed by someone local? See our page for a plumber in Newham for borough-specific coverage and response times.