Why is my water heater leaking?
Where the water is coming from tells you almost everything: top or fitting leaks are usually a $50–$200 DIY or minor plumber fix. A leak from the tank seam or bottom rust stain means the tank is failing — and a leaking tank cannot be repaired. Replacement is the only option, typically $1,200–$3,500 installed.
Don't ignore a water heater leak, even a slow one. A failed tank can dump 40–50 gallons of water quickly and cause significant floor, drywall, and cabinet damage — far more expensive than the replacement itself.
Most likely causes
| Cause | How to tell | The fix | Typical cost |
|---|---|---|---|
| Loose inlet or outlet fitting at the top | Visible drip or moisture at the cold-in or hot-out pipe connections on top of the tank; no rust on the tank body itself | Tighten the fitting with a pipe wrench or replace the dielectric nipple — a DIY fix if you're comfortable with basic plumbing tools | $0 – $80 |
| Temperature and pressure (T&P) relief valve dripping | Water dripping from the valve on the side of the tank or running down the discharge pipe to the floor; T&P valve is the lever-topped valve about 6 inches down the side of the tank | A dripping T&P valve means either the valve itself has failed (replace for $15–$30 in parts, $100–$200 with labor) or your system pressure is genuinely high — a plumber should check pressure before assuming the valve is just faulty | $100 – $250 |
| Drain valve leaking | Water dripping from the spigot-like valve near the bottom of the tank; usually a slow drip | Tighten the valve cap or replace the valve — often caused by corrosion or a bad washer. A minor repair | $20 – $150 |
| Condensation mistaken for a leak | Moisture on the outside of the tank on a humid day or when hot water demand is high; tank is new or newly filled with cold water; not a continuous drip | Condensation on a new or cold-fill tank is normal and dries on its own within a day or two. Wipe the tank and recheck in 24 hours before assuming it's a leak | $0 |
| Tank seam or corrosion leak — tank failure | Water pooling consistently at the base of the tank; rust stains on the tank body or floor beneath it; water that looks rust-colored or discolored at hot water taps | A leaking tank cannot be patched or repaired — the inner lining has failed and the tank must be replaced. This is not a 'wait and see' situation: a failing tank can breach suddenly and flood the area | $1,200 – $3,500 installed (tank replacement) |
Try this first (before you pay anyone)
- Locate where the water is actually coming from before doing anything. Dry the tank exterior with a towel, then look at the fittings on top, the T&P valve on the side, the drain valve near the bottom, and the seam of the tank itself. Different sources require completely different responses.
- If you see water at the top connections, try hand-tightening the fitting first. If the fitting turns, it was loose — monitor for 24 hours to confirm the leak has stopped.
- If the T&P valve is dripping, do not tie the lever shut or cap the valve — that's a safety hazard. The valve is there to prevent the tank from building dangerous pressure. Call a plumber to replace the valve and check system pressure.
- If water is coming from the tank body itself — rust stain, seam moisture, or pooling beneath the tank — turn off the cold-water supply valve above the tank immediately, then call a plumber. Shut off the gas or breaker as well. Don't wait.
Call a pro when…
- Water is coming from the tank body, seam, or you see rust staining — this is a tank failure and same-day service is warranted to prevent flooding
- The T&P relief valve is dripping continuously — the valve may need replacement, or your water pressure is too high (above 80 PSI), which a plumber needs to diagnose
- Discolored or rust-colored water is coming from hot taps — the tank's anode rod has failed and the tank interior is corroding
- The leak is at a connection you've already hand-tightened and it won't stop — the fitting or pipe thread is corroded and needs replacement
Repair or replace?
The repair vs replace decision is straightforward for water heater leaks: if the leak is from a fitting, valve, or connection — repair it, even on an older tank, as long as the tank body itself is sound. If the leak is from the tank — replace it, regardless of age. A leaking tank has no repair. A new 40–50 gallon tank water heater runs $1,200–$3,500 installed; tankless units run $3,000–$6,500 installed. Tankless is worth the premium for households with high hot water demand or gas lines that can support the load.
Want a pro to look at it?
Free, no-obligation — we connect you with one matched local plumbing pro, not a call list.
Related questions
Can a leaking water heater be repaired?
It depends entirely on where the leak is. Fittings, valves, and connections can all be repaired for $50–$250. A leak from the tank body itself — the steel shell — cannot be repaired. The inner glass lining has cracked and the tank will continue to deteriorate. Replacement is the only option.
How urgent is a water heater leak?
A slow drip from a fitting or T&P valve is not an emergency but should be addressed within a few days. Water coming from the tank body is urgent — schedule same-day service. A failing tank can rupture and release 40–50 gallons of water into your home, causing thousands of dollars in floor, drywall, and cabinet damage. Turn off the water supply to the tank while you wait for a plumber.
Why is my water heater leaking from the bottom?
Pooling at the base is either the drain valve (usually a slow drip at the spigot fitting) or the tank seam. Dry the area, wait 30 minutes, and look carefully at where the water originates. Drain valve leaks are minor fixes. Tank seam leaks mean replacement — the difference matters a lot for your next phone call.
What is the T&P relief valve and why is it leaking?
The temperature and pressure relief valve is a safety device required by code on every water heater. It opens automatically if the tank pressure or temperature gets dangerously high. A dripping T&P valve usually means the valve has worn out and needs replacement ($100–$250), but it can also mean your home's water pressure is chronically too high — a plumber should check both before replacing the valve.