Trace the water to its exact source before assuming the tank has failed — most leaks come from a connection or a valve, not the tank itself. The pressure relief valve, the drain valve, and the supply line connections are all common, repairable leak points. Water coming from underneath the tank body itself, however, usually means internal corrosion and points toward replacement rather than repair.
Locate the source before doing anything else
On an electric unit, switch off the breaker. On a gas unit, at minimum turn the gas control to pilot or off per the label. Close the cold water supply valve at the top of the tank, or use your main shut-off — see how to shut off your water if you are not sure where that is.
Dry the area around the tank with towels, wait a few minutes, then look carefully for where water first appears. Each of the following points has a distinct location, which is the fastest way to identify the cause.
Common causes
| Location | Likely cause | How likely |
|---|---|---|
| Pressure relief valve or its discharge pipe | Valve doing its job (excess pressure), or a failed valve | Very common |
| Drain valve near the base | Not fully closed, or worn washer | Common |
| Top of the tank, at pipe connections | Loose fitting or worn washer on the inlet or outlet | Common |
| Anode rod access port | Seal not fully tightened after a recent anode replacement | Occasional |
| Underneath, from the tank body itself | Internal corrosion — the tank is failing | Occasional, more common on older units |
| Condensation on the tank exterior | Not a leak — normal in humid conditions on cold-water tanks | Common, easily mistaken for a leak |
Working through each source
- Check the pressure relief valve first
This valve is designed to open and discharge water if pressure or temperature inside the tank gets too high — it is a safety device doing its job, not necessarily a fault. If it discharges occasionally, that can be normal, particularly on a closed plumbing system. If it drips continuously, the valve itself has likely failed and needs replacing, or the tank’s thermostat is set too high and causing excess pressure.
- Check the drain valve
Located near the base, confirm it is fully closed. These are usually plastic and can develop a slow drip as their internal washer wears — often fixable by simply replacing the valve.
- Check the top connections
Inspect where the cold inlet and hot outlet pipes connect to the tank. A loose fitting can often be tightened carefully by hand or with a wrench; do not overtighten, as that can crack a fitting rather than seal it.
- Rule out condensation
On a tank receiving cold water in a humid room, condensation forming on the outside of the tank is completely normal and easily mistaken for a leak. Dry the tank exterior fully and check again after an hour — condensation reappears as a general film, while a genuine leak reappears as a specific wet point or trickle.
- Check the anode rod port if recently serviced
If the anode rod has been replaced or inspected recently, a leak at its access point on top of the tank often just means the fitting needs to be tightened further.
If it is the tank itself
Water emerging from underneath the tank body, with all connections, valves and the relief valve confirmed dry, points at internal corrosion having breached the tank wall. This is not repairable — a corroded tank needs replacing, not patching. On a unit that is already within a few years of the end of its typical service life, this is often the point where a full replacement is the sensible next step rather than chasing further diagnosis.
If you have confirmed a genuine tank leak, close the cold water supply to the unit and switch off its power (electric) or turn the gas control to off (gas) until it can be replaced. A leaking tank left running can fail more seriously with little warning.
When to call a plumber
Call a plumber for a relief valve that will not stop dripping after checking the thermostat setting, for a drain valve that needs replacing, for any connection leak you are not confident tightening yourself, and for any confirmed tank leak, which will need a full replacement rather than a repair.
Stop and call a qualified appliance technician or electrician if you find scorched or melted wiring, smell burning, see water that has reached electrical components, or if the fault returns immediately after a repair. Never bypass a safety device — thermal fuses, door interlocks and flood switches fail for a reason, and defeating one converts a broken appliance into a fire or flood risk.
