What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Kingdom
Close, not identicalstopcock
also stop tap, internal stop valve, external stopcock
"Stopcock" names both the supplier's valve at the boundary and the occupier's inside the building, so the word alone does not say which — and only one of them is yours to operate.
Australia
Close, not identicalstop tap
also water meter valve, isolation valve
Australian practice usually pairs the boundary valve with the water meter, so the outdoor isolation point is commonly described by the meter rather than by the valve.
United Statesyours
Close, not identicalshut-off valve
also main shut-off, curb stop, water meter valve
The boundary valve is a "curb stop", operated by the utility with a key — a specific term with no British equivalent word, though the British external stopcock is the same idea.
Canada
Close, not identicalshut-off valve
also main shut-off, curb stop
As the United States, with the curb stop normally the utility's to operate and freezing depth driving how deep the boundary chamber sits.
The governing standard, by market
United Kingdom
Water Supply (Water Fittings) Regulations
Requirements for fittings, including isolation and backflow prevention.
United States
IPC / UPC
Water service and distribution requirements, including shut-off provision.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Which valve is mine to turn off?
- The internal one, almost always — and knowing which is which before there is water on the floor is the point of the distinction. A building normally has two isolation points: one at or near the boundary, in a chamber under the footway or the drive, which belongs to the water undertaker and is often operated with a long key; and one inside, usually where the supply first enters, which is the occupier's. Turning the internal valve isolates the building. The boundary valve is the supplier's, may serve more than one property, and in some jurisdictions operating it without authority is an offence — so the practical advice is to find and label the internal one, and to check it actually turns before it is needed.
- Why does an old stopcock often refuse to turn?
- Because it has not been moved in years and its working parts have seized or bonded. A valve left in one position for a long time collects scale and corrosion around the spindle and the seat, and the washer can adhere to the seating; forcing it then either shears the spindle or tears the washer, so a valve that will not turn becomes a valve that will not seal. The standard advice is to exercise the valve periodically — a full close and open once or twice a year — which keeps it free and reveals the failure at a convenient moment rather than an inconvenient one. It is also why plumbers routinely fit a new isolation valve when working on an old supply rather than trusting the existing one.
- What is a service valve, and is it the same thing?
- No — service or isolation valves are the small local valves fitted at individual fittings and appliances, so that a tap, a cistern or a washing machine can be worked on without shutting the whole building down. They are a different scale of device from the main stop valve and they are not a substitute for it: a building with isolation valves everywhere still needs one point that stops the supply entirely. The related distinction is the drain-down provision — a drain cock at the low point that empties the system once it is isolated, which is what actually lets pipework be opened. Isolating without draining leaves the standing water in the pipe to arrive on the floor.