A shut off valve is a plumbing fixture installed on toilets, sinks and other major water lines throughout a building. When a water supply is leaking or repairs are necessary to a water line, it's important to be able to access the shut off valves and know how to locate them. It's always best to shut off the valve that is closest to the issue; if the toilet needs repairing, it's best to shut off the valve located behind the toilet, rather than shutting off the main water supply.
Determine where the water needs to be shut off. If you are shutting the water off to a specific sink or toilet, look for that specific water shut off valve.
Look under the sink or behind the toilet. The shut off valve is located along the pipe water lines, one for hot and one for cold. The valve is identified as a small knob that can be turned on and off.
Locate the main water shut off valve if water to the entire house needs to be shut off. Locate the water heater; the shut off valve will be connected to the cold-water pipeline. The valve looks like a small red knob similar to the one found under the sink or behind the toilet.
Twist the valve to the "off" position to turn the valve off. If the valve is stubborn, a wrench may be used to twist the valve.