Water heater leaking from the bottom: how urgent?

Find out where the water is actually coming from

Not every puddle is a dead tank, and the difference is worth two minutes of looking. Dry everything, put down paper towel, and watch.

Water from the top of the tank is usually a fitting: a cold inlet, a hot outlet, or a failed nipple. That is a repair. Water from a pipe running down the side is often the temperature and pressure relief valve doing exactly its job, which means the real problem is excess pressure or temperature in the system, not the heater shell. Water from a small tube ending near the floor is the same valve discharging through its required drain line. Condensation on a very cold inlet in a humid basement can also collect underneath and look alarming while meaning nothing.

Water appearing at the seam where the jacket meets the floor, with nothing wet above it, is the bad one. Tank water heaters fail from the inside out. The glass lining cracks, the sacrificial anode rod is used up, and the steel underneath corrodes until it perforates. Once it perforates, there is no repair. The tank is a consumable and it has been consumed.

What to do in the next ten minutes

Close the cold water shut-off valve on the inlet at the top of the heater. If it will not turn or there is not one, close the main house shut-off. On a gas heater, turn the gas control knob to off. On an electric heater, switch off the dedicated breaker, and do this before anything else if there is standing water on the floor near it. Do not drain a hot tank onto a finished floor in a hurry; hot water at storage temperature scalds.

Then move what is on the floor. The most expensive part of a water heater failure is almost never the water heater. It is the drywall, the flooring, the stored boxes, and, in a finished basement, the remediation that follows if the water sits.

Why the timing is not negotiable

A perforation in a steel tank under supply pressure enlarges. The corrosion that made the first hole is present across the whole bottom of the tank, and the water flowing through the hole accelerates it. A tank that is beading a slow drip on Monday is a plausible flood on Friday. There is no version of this where waiting improves the outcome, and the difference between a scheduled replacement and an emergency call is a real amount of money.

Age tells you how much benefit of the doubt to give it. Read the serial number on the label; most manufacturers encode the build date in the first four characters. A leaking tank over eight years old is a replacement decision and not worth diagnosing further. Under four years, it may well be under a manufacturer tank warranty, which usually covers the tank and not the labor, so keep the label photographed before it goes.

Replace it properly while it is out

A changeout is the one moment when the surrounding items are cheap to fix. A drain pan piped to a drain, an expansion tank where the house has a backflow preventer or pressure reducing valve, a correctly sized and terminated relief discharge line, seismic strapping where the jurisdiction requires it, and a pair of accessible shut-offs. Each is a small cost during the job and a large one afterward.

This is also the moment to decide whether you want another tank at all. That question, and the arithmetic behind it, is on our page about tank and tankless replacements.

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We publish the computed labor figure above and the plumbing contractors on record in your area, listed alphabetically, never ordered by anything commercial. We do not publish equipment prices, because they vary by capacity, fuel, venting, and local labor. Where another organisation publishes a range, it is linked below rather than reproduced here.