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Water heater leaking from the bottom: what to do
Quick answer
Treat any water heater leak as urgent, because a small drip can become a failed tank and a flooded room with little warning. Shut off the cold water supply to the heater first, then cut gas or electricity to the unit. Do not just mop and watch it. Once the water is stopped, find where the drip actually starts, because valves can be replaced, but a corroded tank cannot be repaired.
Causes, most likely first
Drain valve dripping
Beginner check. The drain valve near the bottom sometimes weeps after being used for flushing, or its washer wears with age, leaving a slow drip that looks like a tank leak. Dry the valve and watch it closely. A valve that drips from its spout can sometimes be snugged or capped temporarily, but one dripping around its stem needs replacement.
Tank corrosion and failure
Pro only, replacement. Steel tanks rust from the inside once their protective anode rod is used up, and the first sign is often a seep at the bottom seam that grows over days. Rusty water, dampness under the tank, and an age past ten years all point the same way. There is no patch or sealant fix. A corroded tank must be replaced.
Relief valve discharge running down
Beginner check, pro repair. The temperature and pressure relief valve opens if temperature or pressure gets too high, and its discharge pipe usually ends near the floor, so the puddle appears at the bottom. Water that is hot, or a valve that keeps releasing, signals a real pressure problem. Never plug or cap that pipe. Call a plumber the same day.
Inlet or outlet connection leaking
Intermediate. A slow leak at the cold inlet or hot outlet fitting on top can run silently down the side of the tank inside its jacket and pool at the base, mimicking a bottom leak. Dry the whole unit, then feel each top fitting and watch for the highest wet point. The true source is always the highest place you find water.
Condensation in humid weather
Beginner. In a humid basement or garage, a tank full of fresh cold water can sweat heavily on a hot day, leaving a puddle that looks exactly like a leak. This happens most after heavy hot-water use refills the tank with cold water. Dry everything, wait a few hours without using hot water, and check whether moisture returns evenly across the surface.
Shut it off first, in this order
- Turn the cold water shutoff valve above or beside the heater clockwise until it stops.
- For gas, turn the control knob to off. For electric, switch off the water heater breaker.
- If water is reaching outlets, drains, or stored items, shut the main house water valve too.
- Drain a few gallons from the drain valve with a hose only after the supply is off, to lower pressure.
- Keep power and gas off until the source is confirmed and repaired.
When to call a pro
- Water is actively pooling, spraying, or the leak is getting worse by the hour
- Any rust at the bottom seam, or the tank is over ten years old
- The relief valve discharges repeatedly or the water is scalding hot
- You cannot find the shutoff, or the shutoff valve itself will not close
- The leak is at a gas control, vent, or electrical connection
- There is ceiling, wall, or floor damage spreading from the leak
What the repair typically costs
Directional national ranges for US homeowners. Your city and system age will move these.
| Repair | Typical cost |
|---|---|
| Emergency service call | $100 to $300 |
| Drain valve replacement | $150 to $350 |
| Relief valve replacement | $200 to $450 |
| Inlet or outlet fitting repair | $250 to $600 |
| New 40 to 50 gallon tank, installed | $1,200 to $2,500 |
| Water damage cleanup after a major failure | $1,000 to $5,000 and up |
Questions homeowners ask
Can I still use hot water if the leak is small?
No. Keep the supply and heat off until the source is known. A tank that is starting to fail can open up suddenly, and running it also feeds the leak continuously.
How fast can a leaking tank flood a room?
A split tank can release its full 40 to 50 gallons in minutes, and the supply line keeps refilling it until the shutoff is closed. That is why closing the valve matters more than mopping.
Should I drain the whole tank right away?
Only if it is safe to do so and the supply is already off. Scalding water and a failing tank make full draining risky for beginners. Most homeowners should stop the water and let the plumber drain it.