Most houses have at least two stopcocks. One is an internal stopcock – the one inside the house that is turned off during many types of maintenance work on the internal plumbing system.
An internal stopcock is typically installed under a sink in the kitchen or utility room. In older houses, they may be in another room or cupboard – or even in the garage or an outhouse!
In some cases, the water meter is close to the internal stopcock.
If you need to use a stopcock key, take care not to damage the meter.

External stopcocks
The other type of stopcock is an external stopcock, usually located below ground level beneath a metal cover on the property boundary.
In some cases, it may be some distance from the house, perhaps below the pavement beside the nearest road.
You would need to turn off an external stopcock if the pipe between the external and internal stopcocks needed repairing or if you were replacing the internal stopcock.
Like some internal stopcocks, an external stopcock is sometimes side-by-side with the water meter.
Take care not to damage the water meter when using a stopcock key.

Types of stopcock head
Stopcocks have one of three types of ‘head’ – the part that the hand or key grips to turn the stopcock on or off.
A crutch head, or crutch ‘pattern’, stopcock looks like a traditional T-shaped tap.
A square head stopcock can usually only by adjusted by a key as there is little for the hand to grip.
The third type is the wheel head valve. This is not usually a mains water stopcock but one which controls an individual part of a plumbing system inside a property, such as the flow of hot water to taps.
Stopcocks have an inlet side – to which the pipe coming from the mains water supply is connected – and an outlet side, connected to the pipe which takes the water from the stopcock and into the property.
The diameter of the inlet side may be the same as that of the outlet side, or sometimes the inlet diameter may be bigger than the outlet, as shown here.