Water heater leaking or a puddle underneath

Water near a water heater can be harmless condensation, a loose fitting or drain valve, a relief valve doing its job, or a tank that has failed. Where the water is and whether it comes back tells you which.

Also searched as: water heater leaking from bottom, water heater leaking from top, water heater leaking from pressure relief valve, water heater leaking what to do.

Before you start. If you smell gas, leave and call 911 and your gas utility from outside. For an active leak, A. O. Smith says to turn off the power or gas and the water supply to the heater.

A residential water heater in a garage with a puddle of water at its base

Every question and answer on this page, in order

Question 1: Do you smell gas, a rotten-egg odor, near the heater?

Yes, or I'm not sure: Leave now: possible gas leak
No: go to question 2

Question 2: Dry the floor and the tank with a towel, then use a flashlight. Where does the water come from?

The relief (T&P) valve is the lever valve near the top or side with a pipe running down toward the floor. The drain valve is the faucet-like valve near the bottom.

Out of the end of the relief valve's discharge pipe: Call a plumber: the relief valve is discharging
From the drain valve near the bottom: Likely cause: a drain valve that is loose or worn
From pipe fittings on top of the heater: Likely cause: a loose or corroded pipe connection
From under the tank, with no source I can see: go to question 3

Question 3: Leave it dry and check again over the next several hours. What happens?

It dries up, and only reappears after long hot-water use: Probably normal: condensation
It keeps coming back and the puddle grows: Likely cause: a leaking tank

Possible results

Need the words for the phone call? Build a what-to-tell-the-plumber checklist, or read when to call a plumber.