How to find and shut off your water main

Why this matters more than anything else here

Nearly every catastrophic domestic water loss we attend has the same shape: water ran for a long time because nobody could stop it. Not because it could not be stopped — because the person there did not know where the valve was, or the valve would not turn.

A supply line under pressure delivers water continuously. The difference between shutting it off in two minutes and in forty is frequently the difference between drying a room and rebuilding a floor.

Where it usually is

The main shutoff sits where the supply enters the building, on the street side of the water meter. On Long Island that typically means one of:

• The basement, on the wall facing the street, often near the front foundation wall
• A utility or mechanical room, near the water heater or boiler
• A crawl space, on properties without a basement — common on the South Shore and East End
• A garage or utility closet in slab-built houses with no basement, such as Levitt-era construction
• An outside meter pit near the property line, under a metal or plastic cover — that valve is the utility's and usually needs a curb key

Follow the pipe. Find the water meter, then look at the pipe on the side the water comes from. The valve on that side is your main.

The two types of valve

A ball valve has a lever handle. A quarter turn, so the handle sits across the pipe rather than along it, closes it. These are reliable and easy.

A gate valve has a round wheel handle. Turn it clockwise, several full rotations, until it stops. These are older and are the ones that seize, snap or fail to seal after years without use.

If you have a gate valve that has not been touched in a decade, there is a fair chance it will not close fully when you need it. That is worth knowing in advance rather than at 2am.

Test it — properly, once

1. Open a tap somewhere in the house

   So you can see the effect.

2. Close the main fully

   Quarter turn for a lever, clockwise to the stop for a wheel. Do not force a seized wheel valve hard — a snapped stem turns a test into an emergency.

3. Check the tap stops

   It should run down to a trickle and then stop. If water keeps flowing, the valve is not sealing and needs a plumber.

4. Open it again slowly

   Slowly, to avoid a pressure surge through the system. Then check for weeping around the valve stem, which is common on old valves that have finally been moved.

Do this once a year. It takes five minutes and it is the cheapest insurance in this entire guides section.

Local isolation valves

Shutting the whole house off works, but it is not always necessary. Most fixtures and appliances have their own valve:

• Under sinks — usually two small valves on the supply pipes
• Behind toilets — one valve on the wall or floor
• Behind the washing machine — hot and cold, and worth turning off when away
• At the water heater — a valve on the cold inlet
• At the dishwasher and refrigerator ice maker

Isolating locally lets the rest of the house keep working while you deal with one failure. But if you are unsure, or the water is arriving faster than you can think, close the main. Nobody was ever harmed by shutting off too much water.

Make sure someone else knows

Show every adult in the household, and anyone who stays there alone. Take a photograph of the valve on your phone so you can send it to a caretaker, a tenant or a family member at short notice.

If the property is seasonal or rented, put a printed note near the valve and give the location to whoever holds keys. The person who finds the leak is frequently not the person who knows the house.

If you need help now

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