Water heater leaking. What to do in the first ten minutes.
Two valves and one switch stop most of the damage. Do those first, then work out where the water is coming from.
Updated October 2026
Shut the water
Find the cold water pipe going into the top of the heater and close the valve on it. Massachusetts code puts that valve near the heater and above the top of the tank, so look up, not down at the floor. A lever handle turns a quarter turn until it sits across the pipe. A round handle turns clockwise until it stops.
If the valve is seized or you cannot find it, close the main where the water line comes into the house.
Shut the heat
On a gas heater, turn the dial on the gas control at the bottom of the tank to OFF, or close the shutoff on the gas pipe beside it. On an electric heater, switch off its breaker at the panel.
If you smell gas, do none of this. Leave the building and call from outside: 911, then National Grid at 800-233-5325 or Eversource Gas at 800-525-8222, whichever is your gas company.
Find where it is coming from
Dry the tank with a towel and watch where the water comes back.
| Where the water shows | What it usually is | Fixable |
|---|---|---|
| Pipe fittings on top | A loose or corroded connection | Often, by tightening or replacing the fitting |
| The small pipe running down the side to the floor | The relief valve letting water go, usually because pressure in the house is too high | Yes. The cause has to be found, not just the valve swapped |
| The drain valve near the bottom | The valve is not closing | Yes, with a new valve |
| A puddle under a heater installed this week | Usually condensation | Nothing to fix |
| The base of the tank, or from under the jacket | The inner tank has rusted through | No |
The last row is the one that matters. A. O. Smith, Rheem and Bradford White all say that a leak from the tank itself means replacement, not repair. A patch on a rusted tank does not hold.
If it keeps coming
Closing the cold valve stops new water going in. It does not empty the 40 or 50 gallons already in the tank. If the leak is steady, screw a garden hose onto the drain valve at the bottom, run the hose to a floor drain or outside, and open the valve. Open a hot faucet somewhere in the house so air can get in and the tank will drain.
The water is hot. Keep children and pets away from the hose end.
If the heater is on an upper floor or in a condo, the water is already on its way to someone else. Read this next.
Once the water is stopped, the floor and walls have about two days to dry before mold starts. What to do about the water that got out.
What to have ready when you call
Gas or electric. The gallons, which is printed on the label on the side of the tank. Where the heater sits, and how a new one gets carried to it. And the age if you know it. The serial number tells you.
Ask for the price before anyone drives over, and ask what it includes. What a replacement costs and what belongs in the quote.
What the plumber is required to do
In Massachusetts only a licensed plumber can replace a water heater, and the work needs a permit from the town's plumbing inspector. A gas heater needs a gas permit as well.
A leaking tank at night does not have to wait for town hall to open. The state rules let a licensed plumber do emergency work first, as long as the inspector is notified and inspects no later than the next working day. So a same-day replacement and a permit are not in conflict. Ask for the permit number afterward.
Before the old tank leaves
Take photographs of the leak, the label and any damage to the floor, walls or belongings. A homeowners policy generally covers the damage a sudden leak causes. It does not pay for the heater itself.
When the new one is in, four small jobs help it last.