It is important that as a householder you know where the incoming mains water supply stop valve is located.
The incoming mains water is a high pressure potable (drinking water) supply bringing water in to your property from the Water Company’s mains water supply in the road. Often it is located under the sink in a kitchen or utility room, cloakroom or some other ground floor location (except for flats).
In the event of a burst pipe or leak in your plumbing system this should be the first valve you shut off as it is high pressure and will create a lot of flood damage in a very short space of time. Next time you have a plumber working in your house/property be sure to ask him where your stop valve is located.
A useful tip; when going away on holiday be sure to trun the water off at the stop valve to protect your property from prolonged serious flooding.