Main shut-off valve

Short definition

The main shut-off valve is the valve that stops all water entering your house. Most Washington homes have two: the inside main shutoff just past the meter, controlled by you, and the curb stop in the public right-of-way, controlled by the utility. Knowing where both are — and which to use when — is the most important plumbing knowledge a homeowner can have.

What it is

“Main shut-off valve” is the search-term umbrella for any valve that turns off all water to the building. Trace your supply path:

1. Water leaves the public main under the street.
2. Runs through a service line toward your house.
3. Passes a curb stop in a buried stop box, just inside the public right-of-way. Utility-owned, operated with a long curb key.
4. Passes the water meter, often in a buried meter pit or sometimes inside the building.
5. Enters the house and meets the inside main shutoff, just past the wall penetration. This one is yours.

In a leak emergency, the inside main shutoff is what you reach for first. It’s quicker, it doesn’t require a special tool, and you don’t have to dig through landscaping to find it. The curb stop is the backup when the inside main is stuck or broken.

Why it matters to a homeowner

Half of plumbing emergencies start with a homeowner running through the house trying to figure out which valve to turn. Five minutes of searching is five minutes of water in your floors. Three things to do today:

• Find your inside main shutoff — typically just inside the foundation on the supply side, at the water heater, or in a utility closet. Tag it.
• Find your curb stop — usually a small round metal lid in the front yard or sidewalk, marked with a “W” or with the utility name. If it’s paved over, your utility can locate it.
• Test the inside main once a year. Off, on, done. If it won’t turn or doesn’t close fully, replace it before you need it.

When a plumber’s quote talks about “main valve replacement” or “shutoff upgrade,” they’re almost always talking about the inside main. When a utility says they’ll “shut off at the curb,” they mean the curb stop.

When you’ll encounter this term

• A burst pipe — the search you’d never want to perform fast.
• Vacation prep — turning off the main and draining the lines to prevent freeze damage while away.
• Long-term renter realizing they’ve never been shown the shutoff — landlord call.
• Pre-purchase home inspection — the inspector will document the location.
• Toilet or fixture replacement when angle stops are missing or broken — turn off here as a fallback.

Common variants and what the main shutoff is not

• Main shut-off vs. fixture shutoff. Fixture shutoffs (angle stops) isolate one sink, toilet, or appliance. The main isolates the whole house.
• Main shut-off vs. hose-line shutoff. Some Washington homes have a separate valve that isolates the outdoor hose-bib branch for winterizing — that’s not the main.
• Main shut-off vs. water heater shutoff. Heater isolation valve only stops water to the heater.
• Inside main vs. curb stop. Both are “main” valves but ownership and access differ — yours vs. utility’s.

FAQ

Where is my main water shut-off valve?

In most Washington homes, look in this order: the basement or crawlspace just inside the foundation on the side facing the street; at the water heater inlet; in a utility closet near the meter (manufactured and modular homes). It’s typically a 3/4-inch or 1-inch valve on the first major pipe entering the house. If you can’t find it indoors, your utility can show you the curb stop in the right-of-way.

How do I shut off water to my entire house?

Find the inside main shutoff. If it’s a quarter-turn ball valve, turn the lever 90 degrees so it’s perpendicular to the pipe — closed. If it’s a multi-turn gate valve, turn the round handle clockwise until it stops, gently. Run a faucet for a minute to confirm flow is dropping. If the inside main won’t turn, call your water utility for a curb-stop shutoff.

What’s the difference between the inside main and the curb stop?

Both shut off all water to the house. The inside main is a valve you own, located just inside the building, that you can turn by hand. The curb stop is owned by the utility, located in the public right-of-way, and operated with a long key. Use the inside main first; the curb stop is the fallback if the inside main is broken or seized.

Can I shut off the curb stop myself?

In a real emergency — water actively flooding the house — most Washington homeowners do, with a curb key. For routine work, most utilities prefer to do it themselves to avoid damaging old valves and to manage liability. Call the utility for non-emergency shutoffs; they’re usually same-day and free of charge.