Turn off the toilet supply valve first. It’s the oval or football-shaped handwheel on the wall behind the toilet, close to the floor. Turn it clockwise until it stops. That shuts off water to just that toilet without touching anything else in the house.
If the valve doesn’t respond, or you’re dealing with a sink, or the situation is bigger, keep reading.
Shutting Off a Toilet
The toilet supply stop valve sits on the water line coming out of the wall, usually behind and below the tank. It’s almost always a small oval handwheel, sometimes a flat-head slot for a screwdriver.
Turn it clockwise (righty-tighty) until firm resistance. Flush once to drain the tank, then verify the tank doesn’t refill. If it keeps filling, the valve seat is shot and you’ll need to go to the house main.
Don’t force a stuck valve. If it won’t move, it’s corroded inside and turning hard will snap the stem. Skip to the main shutoff.
Shutting Off a Sink
Under the sink, look for two valves on the supply lines, one for hot and one for cold. Same deal: clockwise to close. These are angle stops (they make a 90-degree turn from the wall to the faucet line).
Turn off both if you’re dealing with a leak anywhere at the faucet, the supply line, or the drain connections. One drip can become a flood if a supply line braid finally lets go.
Check under the cabinet for standing water before you reach in. Some supply line failures spray hard.
Shutting Off the Whole House
You need the main shutoff if the leak is at a pipe (not a fixture), if you can’t find or operate the fixture stop, or if multiple fixtures are involved.
Where to find it:
- Most Bay Area homes: look along the front wall of the garage, usually low, near where the water service enters the foundation. It’s a gate valve (round wheel handle) or a ball valve (lever handle).
- Older homes: sometimes in a utility room or a crawlspace access panel.
- Near the street: the water meter box is in the sidewalk or front landscaping. Inside is the meter valve, which you can close with a flathead screwdriver or a water meter key. This valve belongs to your utility, but you can use it in a real emergency if the house main fails.
Gate valves (round wheel) require multiple turns to fully close. Ball valves (lever) are a quarter-turn from parallel (open) to perpendicular (closed). After you close it, open a faucet somewhere in the house to relieve pressure and confirm the flow has stopped.
If the Shutoff Valve Is Stuck or Corroded
This is a real problem in older homes, especially in the South Bay and East Bay where houses from the postwar building boom are now 50 or more years old. Mineral buildup from hard water will freeze a gate valve that hasn’t been exercised in years.
Don’t try to force it. A corroded valve that hasn’t turned in years can crack or shear the stem under hard torque, which turns a stuck valve into a broken one with water still flowing. Skip straight to the street meter.
If the house main is frozen, the street meter valve is your fallback. Call your water utility’s emergency line too; they can send someone to close the curb stop on their side.
After You’ve Stopped the Water
A few things to do while you wait for a plumber:
- Open a low faucet (like a hose bib outside) to drain remaining pressure from the lines. This reduces slow seepage at whatever failed.
- Take a photo of the failed valve, pipe, or fitting. A plumber will want to see it, and it helps with getting an accurate quote over the phone.
- Check the water heater. If you’ve shut off the house main, a gas heater should be turned to “pilot” or “vacation” mode; an electric heater should have its breaker switched off. Most units can sit for a few hours without issue, but if you’re going to be offline overnight, don’t leave it running normally with no cold supply coming in.
- Document any visible water damage. If drywall, flooring, or cabinets got wet, you’ll want a record for an insurance claim.
When to Call a Licensed Plumber
Shutting off the water is the emergency response. What comes next, diagnosing the actual failure, replacing corroded valves, repairing or replacing pipe, is work for a licensed plumbing contractor.
California licenses plumbing contractors through the CSLB. You can verify any plumber’s license at cslb.ca.gov before they start work. Type in their name or license number and confirm it’s active and in good standing. This takes about 30 seconds and protects you.
Situations where you want a licensed plumber, not a handyman:
- Any pipe that burst or cracked, not just a fitting or supply line
- Corroded shutoff valves that need replacement (working on the valve while water is live requires shutting off the whole street side, which often needs utility coordination)
- Water heater supply connections
- Any leak inside a wall or ceiling
- Main shutoff valve replacement
Get at least two quotes. Ask each plumber for their license number before they visit; a legitimate pro will give it without hesitation. Pricing varies by job scope, materials, and location, so get a written estimate before authorizing anything.
Once the water is off, that’s where your job ends. Call a licensed plumber for everything after that. If your shutoff valves are original gate valves from a house built before 1980, mention it when you call: a plumber can swap them for modern ball valves while the water is already off, so you’re not stuck in this same situation next time.