Your water heater is leaking. What to do right now.

Turn off the power or gas to the heater first, then close the cold water inlet valve on top of it. Doing it in that order matters: an electric element that fires with the tank draining will burn out, and a gas burner heating an empty tank is worse than that.

1. Kill the energy

Electric: switch off the breaker labeled for the water heater. It is usually a double breaker. If nothing is labeled, switch off the main.

Gas: turn the dial on the control valve to “off”, or to “pilot” if there is no off position. The gas shut-off is usually a lever on the pipe going into the control valve, and it is closed when the lever sits across the pipe.

2. Close the cold inlet

There is a valve on the pipe entering the top of the heater, usually on the right. Close it. That stops the tank refilling as it empties, which is the difference between a puddle and a flood.

If that valve will not turn, close the main shut-off for the house instead.

3. Get the water somewhere useful

Attach a hose to the drain valve at the bottom of the tank and run it to a floor drain, a sump, or outside. Open a hot faucet somewhere in the house to let air in, or the tank will drain slowly or not at all.

The water coming out is hot enough to scald for a while. Give it time before you put a hand near the hose end.

What the leak location tells you

From the bottom of the tank itself: the tank has corroded through. This cannot be repaired, and it will keep leaking until the tank is empty. Replace it.

From a fitting on top: often a loose or failed connection, and often repairable by a plumber without replacing the heater.

From the pressure relief valve, the pipe running down the side: either the valve has failed or the tank is over-pressure or overheating. Treat over-heating as urgent and shut the energy off.

A small puddle underneath with no obvious source: condensation is possible in humid weather on a gas heater, but assume a leak until you have watched it dry and stay dry.

Do not relight it

Once the tank is drained or the water is off, leave the heater off until someone has looked at it. A gas water heater firing with a partly empty tank can damage the tank and, at the extreme, is a genuine hazard.

While you wait

You have no hot water, which is inconvenient, and you may have a wet floor, which is the actual problem. Water heaters are usually in a garage, a utility closet, or a basement, which means the water has somewhere to go and something absorbent nearby.

• Get standing water off the floor first.
• Move anything stored on the floor near the heater, especially cardboard.
• If the heater sits over finished space, check the ceiling below.
• Photograph the heater, the connections, and the wet area before anyone starts work.

That last one matters more than it looks. Insurance treats the failed part and the damage differently: many policies pay for the damage the water caused while excluding the heater that caused it.

How long before it matters

If the water reached carpet, drywall, or a subfloor, the clock has started. The window is 24 to 48 hours, and a water heater failure is often discovered late, because it happens in a room nobody sits in.

If the area is small and the water was clean, air movement and time may be enough. If it soaked into anything, or you are not sure how far it traveled, the question of who to call comes down to whether water is still arriving.

The short version

Power or gas off first. Cold inlet valve closed second. Drain to a hose if you can. A tank leaking from the bottom is finished and cannot be repaired. Do not relight it until it has been looked at.