Short answer
The main shutoff is usually where the water line enters the house: on a basement front wall, in a utility closet, in the garage, or near the water heater in slab homes. Find it and test it before an emergency.
Where to look
Follow the water line from the street side of the house. The valve is usually within a few feet of where the pipe comes through the wall or floor.
- Basement homes: on the wall facing the street, near the water meter.
- Slab homes: in a garage, utility closet, near the water heater, or outside on the wall.
- Crawl-space homes: just inside the crawl space access, or outside near the foundation.
- Warm climates: sometimes outside, in a box near the house or at the meter.
Types of valve
A lever (ball) valve is off when the handle is crossways to the pipe. A round-handle (gate or globe) valve turns clockwise until it stops. Old gate valves can seize or break; don't force one.
If you can't find it or it's stuck
The meter box by the street has a shutoff that usually needs a meter key. A plumber can replace a seized main valve with a quarter-turn ball valve so it's easy to use next time.
Questions
Should everyone in the house know where it is?
Yes. Tag the valve and show everyone how to close it. It's the single most useful thing to know in a plumbing emergency.
Is it OK to turn the main valve on and off?
Yes, and testing it once or twice a year helps keep it from seizing.
What should I do if my main water shutoff valve is stuck?
Do not force or strike a seized gate valve with a wrench, as old brass stems can snap and cause a full-volume flood. Spray penetrating oil on the stem, or shut off water at the meter box and have a plumber install a new quarter-turn ball valve.
What tool is needed to turn off water at the city meter box?
A commercial water meter curb key (a long T-shaped steel tool with a slotted end) is designed to reach down into deep meter pits and turn the curb stop valve 90 degrees.
This guide is general information, not professional, legal or insurance advice. Follow your insurer's instructions and local codes, and put safety first.