What Is a Shutoff Valve?

The small valve on the supply line under a sink, behind a toilet, or beside an appliance that cuts water to that one fixture, so a repair does not mean shutting down the whole house. Turn it clockwise until it stops, then open the fixture to drain the last of the pressure before any plumbing work.

Two designs are common: older multi-turn valves that screw down over several rotations, and quarter-turn ball valves whose lever moves 90 degrees from open to closed. Multi-turn valves that sit untouched for years seize up or weep at the stem exactly when you finally need them, which is why plumbers suggest closing and reopening each one once a year, just to keep it moving.

If a fixture has no shutoff valve, or the valve won't budge or drips when turned, use the home's main shutoff instead: usually near where the water line enters the house, at the water heater, or in a basement or crawl space. A seized fixture valve is worth replacing ($8–$15 for a quarter-turn) the next time the water is off anyway, because the day you need it in a hurry is the wrong day to discover it's frozen open.