Water heater leaking

Last updated: 2026-07-17 · Reviewed by the DisasterStatus editorial team

Quick answer: Cut the power to the heater first — the breaker for an electric unit, the gas control or gas shutoff valve for a gas unit — then close the shutoff valve on the cold-water line feeding the tank so it stops refilling. Then figure out where it’s leaking: fittings on top and a failed drain or relief valve are repairs, but water seeping from the bottom of the tank body means the tank has corroded through and the heater needs replacing. And keep one eye on the floor: wet materials must be dried within 24–48 hours to avoid mold growth (EPA).

A water heater is a pressurized tank of 40–50 gallons connected to a supply line that will keep refilling it indefinitely — which is why a leaking heater never fixes itself, and why the first two moves are always the same regardless of the cause. This guide walks through shutting it down safely, reading the leak location, deciding between repair and replacement, and catching the part most people miss: the water that already went into the floor.

Shut it down first: what to do right now, step by step

Power before water, water before diagnosis. For an electric heater the power is its breaker; for a gas heater it’s the gas control knob or the gas shutoff valve on the supply line (A. O. Smith). In order:

1. Cut the power to the heater. Electric: switch off the water heater’s breaker at the electrical panel. Gas: turn the gas control knob on the heater to OFF, or close the gas shutoff valve on the supply line. A heating element or burner running in a draining tank is a hazard, so do this before anything else.
2. Shut off the water supply. Close the shutoff valve on the cold-water line feeding the heater — usually on top of the tank or just above it. If the valve is stuck or missing, close the home’s main water shutoff instead. Until the supply is off, the tank keeps refilling and keeps feeding the leak.
3. Find where the water is coming from. Dry the outside of the tank, then watch: the top (inlet/outlet fittings), the side (the T&P relief valve or its discharge pipe), or the bottom (the drain valve — or the tank itself). Where it leaks decides whether this is a small repair or a replacement.
4. Contain the water and protect the floor. Mop or vacuum up the standing water, move belongings out of its path, and get air moving across the wet area. A typical tank holds 40–50 gallons, so even a “slow” leak puts real water on the floor over a day.
5. Drain the tank if it’s leaking from the tank body. If the tank itself is leaking, attach a garden hose to the drain valve at the bottom, run it to a floor drain or outside, open the valve, and open a hot-water faucet upstairs so the tank can drain. An emptied tank can’t dump its remaining gallons on your floor.
6. Call a plumber — or a restoration pro if the water spread. A plumber handles the heater: fittings, valves, or a replacement. If the water already soaked flooring, drywall, or an adjacent room, you also have a drying problem on a 24–48-hour clock — that part is a water damage restoration job.

Where is it leaking from?

Dry the outside of the tank with a towel, then watch where moisture reappears. Location is diagnosis (A. O. Smith):

• Top of the tank — inlet/outlet fittings. The cold-inlet and hot-outlet connections are the most common and least serious source. Loose or corroded fittings can often be tightened or repacked; a plumber can resolve this without touching the tank.
• Side of the tank — the T&P relief valve. Water at the temperature and pressure relief valve or dripping from its discharge pipe is a special case — see below, because it can be a safety signal rather than a plumbing annoyance.
• Bottom of the tank — drain valve vs. the tank itself. First check the drain valve: if it isn’t closing fully or its seal has failed, it can be replaced. But if the valve is dry and water is seeping from the tank body or pooling underneath with no other source, the inner tank has almost certainly corroded through — and that’s not a repair (more below).
• Or: it’s condensation, not a leak. An even film of moisture that appears when the tank refills with cold water (or when a gas burner first fires) and disappears as the water heats is normal condensation. A real leak persists and reappears at one spot.

If the T&P valve is discharging, pay attention

The T&P (temperature and pressure) relief valve is the tank’s last-line safety device: on residential water heaters it’s built to open at roughly 150 psi or 210°F and vent hot water rather than let the tank fail catastrophically. In normal operation, no water should discharge from it at all — so a T&P valve that drips or periodically dumps water is telling you something. Per valve-manufacturer guidance (Watts), discharge may indicate an unsafe temperature or pressure condition that needs immediate attention from a qualified technician. A common culprit is thermal expansion: heated water expands, and in a “closed” plumbing system (one with a backflow preventer or check valve) that pressure has nowhere to go — the fix is typically an expansion tank, not a new relief valve. Whatever you do, never plug or cap a discharging T&P valve; you’d be disabling the safety device while the underlying pressure problem continues.

Repair it or replace it?

The dividing line is simple: everything attached to the tank is repairable; the tank itself is not. Fittings can be tightened, and the T&P valve, the drain valve, elements, and thermostats can all be swapped. But the inner tank is a welded, glass-lined vessel — once corrosion eats through it, water from the bottom of the heater is “often the first indication of a serious problem,” and the practical solution is replacing the unit, not patching it (A. O. Smith). A tank leak also doesn’t plateau: the corrosion that made the first pinhole keeps working, so a weep becomes a stream on its own schedule. If your heater is leaking from the tank body, shut it down, drain it, and plan the replacement now — on your timing, not the tank’s.

The water damage clock: what the leak already did to the floor

While you’re diagnosing the heater, the water that already escaped is soaking downward — into flooring, subfloor, the bottom plates of adjacent walls, and (for heaters on an upper floor or in an attic) the ceiling below. Water heaters live in closets, garages, and utility corners, so slow leaks routinely run for days before anyone notices, and wet materials must be dried within 24–48 hours to avoid mold growth, according to the EPA. Check beyond the visible puddle: discoloration or swelling at baseboards, cupping floorboards, damp drywall, and musty smell are all signs the water traveled — our guide to signs of water damage covers what to look for, and water damage cleanup walks through the drying process itself.

Plumber or restoration pro — who do you call?

Both, sometimes — they fix different problems. A plumber repairs or replaces the heater: fittings, valves, expansion tank, or a new unit. A restoration pro dries the structure: extraction, removing soaked materials, and running commercial air movers and dehumidifiers until the floor and walls are verifiably dry. If you caught the leak early and the water stayed on a sealed concrete or tile floor, the plumber alone is usually enough. If the water reached wood flooring, carpet, drywall, or a room below — or the leak clearly ran for days — bring in a water damage restoration pro for the drying while the plumber handles the heater. For a tank that let go all at once and is actively flooding the space, treat it like any other flood: see emergency water removal. And before the work starts, it’s worth knowing what water damage restoration costs.