Do this first
- Cut the power or gas. Electric: switch off its breaker. Gas: turn the control knob to off or pilot.
- Close the cold-water valve on the pipe going into the top of the tank. That stops the tank from refilling.
- Watch out for scalding water. Water in the tank can be hot enough to burn for hours after you turn it off.
- Keep electrical cords and outlets away from the water.
Find where the water comes from
Dry the outside of the tank and the floor with a towel, then watch for a few minutes. Start at the top and work down, because water from a fitting runs down the side and can look like a tank leak.
| Where it's wet | What it usually means | What happens next |
|---|---|---|
| Top of the heater, at the pipe connections | A loose or corroded fitting, or a worn connector hose. | Usually a small plumbing repair. Don't overtighten old fittings. |
| The relief valve on the side, or the pipe running down from it | The temperature and pressure relief valve is opening, or it's worn out. | A safety part. Never cap or plug it. A plumber should check pressure and temperature, and replace the valve. |
| The drain valve near the bottom | The valve is loose or its seal has worn. | Often a quick valve replacement. |
| Under the tank, with no fitting above it wet | The tank itself has rusted through inside. | The tank can't be repaired. Plan on a replacement. |
Gas heaters can also drip condensation onto the burner when the tank fills with cold water. That stops once the water heats up and isn't a leak.
If you need a new water heater
A standard tank heater typically costs $600 to $2,500 installed. Tankless models run about $1,400 to $3,900 installed, and switching from a tank to tankless adds labor for new gas lines, venting or electrical work.
Things that move the price:
- Tank size and fuel type
- New gas line, venting or electrical work
- A tight or hard-to-reach location
- Permits, often $25 to $300 depending on where you live
Sources
- NerdWallet, Water Heater Cost, updated September 2025