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Water heater leaking: where it's coming from and what to do

Water around a water heater doesn't always mean the tank is failing. Leaks from fittings, valves and drain lines are often simple fixes. A leak from the tank body itself is the one that usually means replacement. Here's how to stop the damage and track down the source.

Safety first. Water and electricity don't mix: if water is near an electric heater's wiring or the floor is flooded, turn off the breaker before you get close. If you smell gas, leave the house and call your gas utility or 911 from outside. Water from the tank and relief valve can be scalding.

1. Limit the damage right away

Turn off the energy. Electric: switch off the heater's breaker. Gas: turn the control knob to "off" or "pilot," per the label on the heater.
Shut off the cold water supply at the valve on the cold inlet pipe above the heater (usually marked or on the right side). This stops the tank from refilling.
If the tank itself is leaking badly, you can drain it: attach a garden hose to the drain valve near the bottom, run it to a floor drain or outside, and open a hot water faucet in the house to let air in. Let the water cool first if you can.
Dry the area so you can see where new water appears.

2. Make sure it's really the water heater

Condensation can look like a leak, especially on gas heaters right after a big draw of cold water, or on cold pipes in humid weather. Wipe everything dry and watch for an hour. Also check nearby sources: a furnace or AC condensate line, a water softener, a washing machine hose, or plumbing overhead dripping down onto the heater.

3. Find the source: work from the top down

Hot and cold connections on top. Look for drips or corrosion where the pipes connect. Loose fittings can often be snugged up; corroded flex connectors or dielectric nipples can be replaced.
Temperature and pressure (T&P) relief valve. This is the valve on the top or upper side with a pipe running down toward the floor. Water dripping from that discharge pipe means the valve is opening, which can be a worn valve or a real problem: water temperature set too high or pressure in the house too high (for example, from a failed or missing thermal expansion tank on a closed system). Never cap or plug this valve or its pipe. A plumber can test the house water pressure and replace the valve.
Gas heater only: under the burner area. Water dripping inside the combustion chamber can be condensation, but rust and scale there can also mean the tank is failing from the inside.
Electric heater only: element access panels. With the power off, remove the panels and look around the heating element gaskets. A leaking element gasket can often be fixed by replacing the gasket or element (the tank must be drained below that level first).
Drain valve at the bottom. If it drips from the spout, it may not be fully closed, or sediment is keeping it from sealing. Try closing it snugly, or cap it with a hose cap as a stopgap. Leaking drain valves can be replaced.
The tank itself. Water coming from under the heater with none of the above leaking, or rust-colored water seeping from the bottom or seams of the jacket, usually means the inner tank has corroded through.

4. Fixable vs. replace

Usually repairable: loose or corroded supply connections, a dripping drain valve, a leaking element gasket, a faulty T&P valve, or pressure problems that a plumber can correct.

Usually means replacement: a leak from the tank body. Tank leaks generally can't be patched reliably; the heater needs replacing, and a leaking tank can fail suddenly. Check the label for the brand and serial number, which can tell you the age and whether it's still under warranty.

Preventing future leaks

Put the heater in a drain pan piped to a drain, especially if it's in a finished area or attic. Some codes require one in those locations.
Flush sediment per the manufacturer's instructions, particularly if you have hard water.
Ask a plumber about checking the anode rod, which helps protect the tank from corrosion and wears out over time.
Keep the thermostat at a sensible setting (around 120°F is commonly recommended) and have high house water pressure addressed.
Consider a water leak alarm on the floor next to the heater.

Tip: Take a photo of where the water is coming from and of the heater's label before you call. It helps a plumber tell you over the phone whether it's a repair or a replacement.

Heater not leaking but not heating? See Water heater not working: what to check.