Shut off the water and the power or gas first, then trace the source. Water pooling under the tank rarely comes from where it looks like it's coming from. The most likely sources are the drain valve at the bottom, the T&P relief valve discharge tube, the cold inlet or hot outlet connections at the top dripping down, or the tank itself. If water is coming from the bottom of the tank body, the inner liner has corroded through and the tank needs to be replaced, not repaired.
Stop the damage first
- Shut off the water supply at the cold inlet valve on top of the heater, or at the main shutoff if the inlet valve won't turn.
- Shut off power or gas. Electric: flip the dedicated breaker for the water heater. Gas: turn the gas control to "Off" at the unit and shut the gas supply valve on the line nearby.
- Open a hot water faucet somewhere in the house to relieve pressure and let the tank stop pulling in fresh water.
- Put towels and a shallow pan under the leak to limit floor damage.
- Then figure out the source.
Quick checks
- How old is the heater? Tag on the side shows the install date or serial number. Most tank water heaters last 8 to 12 years.
- Is the leak constant or intermittent?
- Where exactly is the water coming from: drain valve, T&P discharge tube, connections at the top, or the tank body itself?
- Is there a drip pan under the heater? Is it overflowing or holding water?
- Is there hard water in your area (white scale on faucets, soap that doesn't lather)?
How to find the actual source
- Dry the entire heater and the floor around it with a towel.
- Wait 10 to 20 minutes with the water and power off.
- Look for where new water appears first.
- If the heater is in an enclosure, use a flashlight to inspect the top connections, the side along the seam, and the bottom around the drain valve.
If the leak is from the drain valve
The drain valve is the plastic or brass spigot near the bottom. It opens when you flush the tank. Two failure modes:
- Not fully closed after a flush. Try snugging it gently.
- Plastic valve cracked or seals failed. Replacement requires draining the tank. A plumber can swap the valve while the tank is empty.
If the heater is otherwise in good shape and under 8 years old, a drain valve replacement is a normal repair.
If the leak is from the T&P relief valve discharge tube
The temperature and pressure (T&P) relief valve is a safety device that opens if tank temperature or pressure gets too high. A pipe runs from it to within 6 inches of the floor. Water dripping from that tube usually means one of:
- Thermal expansion (no expansion tank in a closed plumbing system).
- Pressure too high in the system (often from a failing pressure regulator at the main).
- Temperature set too high.
- The T&P valve itself is failing.
This is a plumber call. T&P valve testing and replacement involves scalding water and a pressurized vessel; we don't write DIY for it. Don't cap the discharge tube. The tube exists so pressurized hot water has somewhere safe to go.
If the leak is from the connections at the top
Cold inlet and hot outlet connections at the top of the tank can leak from loose fittings, failing dielectric unions, or corroded nipples. Water from a top leak runs down the side of the tank and pools at the bottom, which is why "leak at the bottom" sometimes turns out to be a top leak. A plumber can tighten or replace the fittings without replacing the tank.
If the leak is from the tank itself
This is the one that ends the conversation. If water is seeping from the bottom of the tank body, between the outer jacket and the floor, the inner glass-lined steel tank has corroded through. There's no repair. The tank has to be replaced.
Why this happens: minerals in water settle as sediment on the bottom of the tank. Over years, sediment traps moisture against the steel and the glass lining cracks. Once water reaches the steel and the anode rod is spent, the tank rusts from the inside until a pinhole opens. Sediment flushing and anode rod replacement on a regular cadence is how you delay this. See how often should you flush your water heater and water heater anode rod replacement frequency.
When to call a plumber
Almost always for this issue. Specifically:
- Any T&P valve discharge or pressure-related leak.
- Any tank-body leak (replacement).
- Drain valve replacement.
- Connection leaks if you aren't comfortable with copper or PEX work.
- Gas water heater of any leak type if it involves disconnecting gas lines.
- Any leak that's actively pooling on the floor.
Water-heater failures are also among the most common claims that homeowners insurance covers, but only if the leak is sudden and accidental. If you knew about a slow drip and didn't address it, the insurer can deny the claim. Document the leak, the date you noticed it, and the response.
What to consider when replacing
- Age 8 to 12+ years: replace, don't repair.
- Newer tank with a non-tank-body failure: repair is usually cheaper.
- Consider whether a tankless or heat pump water heater fits your hot water demand and budget. Both have longer lifespans (15 to 20 years).
- Add a drip pan under the new heater if there isn't one. Code in many jurisdictions requires it in attics or upper floors.
- Consider a leak alarm or automatic shutoff valve, especially if the heater is upstairs or above a finished space.
Good maintenance rhythm
- Yearly: visual check around the base of the heater for rust, drips, or pan water.
- Yearly: flush sediment per the manual if the tank is healthy.
- Every 3 to 5 years: have a plumber check the anode rod.
- Every 5 years past age 8: assess whether to replace before the tank fails.
- Monthly: glance under the heater. A slow leak you catch in week one is a much smaller bill than the one you catch when it's running across the floor.
- Before any extended trip: shut off the water supply to the heater if it's older than 8 years.