A stop cock is used to control the flow of mains water in both residential and commercial buildings. It is important to know that if you are unfortunate enough to have a burst pipe or broken tap water pouring everywhere causing damage where your stop cock is to halt the water. Generally speaking there is usually an internal and external stop cock in more homes.
External Stop cock
An external valve controls the flow from the water mains serving the street into your house. If this supply develops a leak, then the external stop cock needs shutting off to allow for repairs.
Internal Stop cock
An internal stop cock turns off the water from the supply pipe that enters your property, and can be located in various places.
The stop cock looks like a tap, but without an outlet spout. It's placed between two lengths of pipes, acting as a connector. This allows the stop cock to control the flow of water with the twist of the tap.