Short answer
First, stop the damage: turn off the gas (pilot or off) or the breaker, and close the cold supply valve. Then dry everything and look. Leaks from the top fittings or the drain valve are usually a tightening or part swap. A dripping T&P valve points to pressure, temperature or a worn valve. Water from the tank bottom or body means corrosion, which A. O. Smith says cannot be repaired: replace the heater.
Step 1: make it safe
- Turn the gas control to off, or switch off the breaker.
- Close the cold water supply valve on top of the tank.
- If water is spraying or flowing steadily, close the main water valve and open a hot tap to release pressure.
- Mop up, dry the tank, and put a towel or tray down so you can see where fresh water appears.
Step 2: find the source
Water heater leak sources
| Where | Likely cause | Fix |
|---|---|---|
| Top: cold inlet or hot outlet | Loose or corroded fittings or connectors | Tighten gently; replace the flex connector or dielectric nipple if corroded |
| T&P valve or its pipe | Thermal expansion, high pressure, high temperature, or a worn valve | T&P valve guide |
| Drain valve | Worn washer, not fully closed, or debris in the seat | Close it firmly, flush debris, cap it, or replace the valve |
| Element gasket (electric) | Failed gasket where an element enters the tank | Replace the element gasket |
| Tank body or bottom | Corrosion through the steel | Replace the water heater |
The leak points above follow A. O. Smith’s consumer guide, which also lists rust colored hot water, rumbling and metallic smells as signs of internal corrosion (A. O. Smith). Mr. Rooter’s guide to bottom leaks covers the same split between fixable valves and a failed tank (Mr. Rooter).
Step 3: fix or replace
- Fittings, drain valve, T&P valve, element gasket: worth fixing on a tank that is otherwise sound.
- Tank body or bottom: no repair. Plan a replacement now; costs are in the replacement cost guide. Leave the cold supply off and the heat off until then.
- A tank past about 10 years with any leak: compare the repair against replacing, using the lifespan guide.
Limit the next leak
A drain pan with a drain line catches slow leaks, and a leak sensor in the pan warns you or shuts the water off automatically.
See leak alarms with automatic shutoff
Questions people ask
Is a leaking water heater an emergency?
A slow drip from a fitting is not, but act the same day. A steady stream, water spraying under pressure, or water near the burner or electrical parts is: shut off the heat and the cold supply, and the main water valve if needed.
Why is my water heater leaking from the bottom?
Either the drain valve is dripping, the T&P discharge pipe is releasing water that runs down, condensation is collecting, or the tank itself has corroded through. Dry it, then watch each spot. A corroded tank cannot be repaired.
Can condensation look like a leak?
Yes. A.O. Smith notes condensation can dampen the outside of the tank, especially in humid weather or when cold water first fills a hot tank. Wipe it dry and watch; if water returns within hours, it is a leak.
Should I turn off my water heater if it is leaking?
Yes. Turn off the gas or the breaker so the tank does not heat while empty or partly empty, and close the cold supply to stop more water entering.
Sources
Last reviewed October 29, 2026. Models, codes and listings change; check your heater’s manual and your local code, and follow the maker’s instructions.