A corporation stop is the first valve on a home's water service line. It is tapped directly into the city water main on the utility side. It lets a plumber start a new service line without shutting off the main. Water then flows on to the curb stop and the meter.
A corporation stop is the first valve on a home's water service line. It sits where the service line taps into the city water main. Plumbers also call it a corp stop or corporation cock. In most cities the water utility owns and controls it.
Where it sits and how it taps the main
The corporation stop is threaded straight into the water main. A crew uses a drilling and tapping machine to make a pressure tap while the main stays full and under pressure. The inlet side connects to the main. The outlet side connects to the service line, the pipe that carries water toward the house. This lets a plumber start a new service without shutting the main off for the whole street.
How it fits with the curb stop and meter
The corporation stop is only the first valve in the run. Water leaves the main through the corp stop, travels along the service line, and reaches the curb stop near the property line. From there it flows to the water meter, which the meter yoke holds in place. A simple way to remember the order is main, corp stop, curb stop, meter. The corp stop stays on the utility's side and is not a valve homeowners use.
Material and standards
Corporation stops are usually made of brass. Service brass parts are built to meet the AWWA C800 standard for water service fittings. They come with different inlet and outlet connections to match the main and the service pipe. Because the utility owns and operates the corp stop, most cities ask homeowners not to touch it.