Water Heater Leaking? Do These 4 Things First
A leaking water heater is either a minor fitting problem or the tank itself failing — and where the water is coming from tells you which. Do these four things first, then use the location guide below.
The 4-step immediate response
- Cut the power. Flip the breaker for an electric unit; turn the gas control to OFF for gas. Heating an emptying tank can destroy the elements — or worse.
- Close the cold water supply. The valve is on the cold inlet line at the top of the tank. Clockwise to close.
- Contain the water. Towels, a pan, a wet vac. If water is reaching walls or flooring, see our water damage first-24-hours guide.
- Find the leak's origin — top fittings, T&P valve, drain valve, or the tank body itself. This determines whether you're repairing or replacing.
What the leak location means
| Where it's leaking | Likely cause | Typical cost |
|---|---|---|
| Top — inlet/outlet fittings | Loose or corroded connections | $100 – $300 |
| Side — T&P relief valve | Failed valve or excess pressure | $150 – $350 |
| Bottom — drain valve | Worn valve, easy swap | $100 – $250 |
| Bottom — tank body / seam | Internal tank corrosion | Replace: $1,200 – $3,500 |
| Puddle, tank intact, pilot out | Condensation or flue issue | $0 – $250 |
Why a leaking tank body can't be repaired
The steel tank is glass-lined; once corrosion breaks through, no sealant or weld holds against 40–80 PSI of hot water. A tank-body leak at year 8+ means replacement — standard 40–50 gallon swaps run $1,200–$2,200, power-vent and hybrid heat-pump models $2,000–$3,500+. Full pricing is in our plumbing cost guide.
Is it about to fail? The early warnings
- Rusty or brown hot water (cold runs clear)
- Rumbling or popping as sediment bakes on the tank floor
- Moisture rings or rust streaks under the tank
- The unit is 10+ years old — check the serial number's date code
A $15 leak-alarm puck or a smart shutoff valve under the tank is the cheapest insurance in plumbing — tank failures release 40+ gallons, then keep flowing off the supply line until someone notices.
Frequently asked questions
Can I still use water if my water heater is leaking?
Cold water, yes. But shut off power/gas and the heater's cold inlet valve immediately — a small leak can become a 40-gallon flood, and heating a draining tank can cause serious damage.
How much does it cost to replace a leaking water heater?
A standard 40–50 gallon tank replacement runs $1,200–$2,200 installed in 2026. Power-vent gas models, tankless conversions, and hybrid heat-pump water heaters run $2,000–$4,500+ depending on venting and electrical work.
How long do water heaters last?
Tank water heaters typically last 8–12 years; tankless units 15–20 with annual descaling. Hard-water regions without maintenance trend to the low end.