Underground stopcock won't turn — what to do

The external stopcock (sometimes called the Buffalo box or property stopcock) is the valve in a small underground box near your property boundary that controls your entire water supply. Knowing where it is and being able to operate it is essential in a flood or burst pipe emergency.

Find the box — look for a small metal or plastic lid flush with the pavement or drive, often marked "W" or "Water" or with a blue lid. It is usually within 1 metre of your boundary wall. If you cannot find it, contact your water company who should have records.

To open the lid, use a metal bar or flat screwdriver in the slot. Some older boxes need a specialist stopcock key — a long rod with a square or flat socket at the end (hire from a tool hire company, or your water company may lend one).

If the valve is seized (will not turn with moderate force), do not force it — you may snap the valve stem. Apply penetrating oil (WD-40 or Plus Gas) around the stem, leave for 20–30 minutes, and try again. In some cases the valve needs specialist attention from your water company.

Turn clockwise to close (off), anti-clockwise to open (on). Many external stopcocks are not designed for regular operation and will seize if not exercised occasionally. Once freed, slowly turn it open and closed a few times to exercise it.

If the external stopcock is your responsibility (on your property side of the boundary) and it cannot be freed or is leaking, contact a plumber. If it is on the highway side of your boundary, contact your water supplier — Thames Water, Anglian Water, etc. — as it is their asset to repair.