Two things are true at once: most water heater leaks are not an emergency, and the ones that are will empty forty to eighty gallons onto your floor. You cannot tell which you have from the doorway, so treat it as the second until you know.
The first ten minutes, in order
- Turn off the power or gas. Electric: the breaker labelled for the water heater. Gas: the dial on the thermostat to "off" or "pilot". A heating element running in a draining tank destroys it and can be dangerous.
- Turn off the cold water supply. A valve on the pipe entering the top of the tank. If it will not turn, use the main shut-off for the house.
- Do not open the drain valve unless you know where the water will go. A hose to a floor drain or outside, or nowhere at all.
- Get water off the floor and things off the floor. Cardboard, anything wooden, anything with a motor in it.
- Photograph it, with the date. If this becomes an insurance claim, the picture taken before you cleaned up is the one that matters.
Two things that are not a normal leak. If the tank is bulging or deformed, or if the temperature and pressure relief valve is discharging steam or hot water, leave the area and call a plumber immediately. Those are pressure problems, not water problems.
Where it is leaking tells you what it is
| Where | Likely cause | Usually means |
|---|---|---|
| Top, around the pipe fittings | Loose or corroded connection | Repairable, often cheaply |
| The relief valve on the side | Valve failing, or the pressure is genuinely too high | Repairable — but find out which of the two it is |
| The drain valve at the bottom | Valve not seated, or worn | Repairable, sometimes just needs closing properly |
| Underneath the tank itself | The tank has corroded through | Replacement. Tanks are not repairable once they go. |
| Only when hot water runs | A pipe or fitting, not the tank | Repairable |
The useful diagnostic if it is not obvious: dry everything thoroughly, put down paper towel, and come back in an hour. Water finds the lowest point, so what looks like a tank failure is frequently a fitting above it.
Repair or replace
Age decides most of this. A tank water heater typically lasts eight to twelve years, and the serial number on the label usually encodes the manufacture date. Past about ten years, spending several hundred dollars on a repair buys you an unknown amount of time on a component that is going to fail anyway.
Costs vary a great deal by region, by whether it is gas or electric, and by whether the installation needs bringing up to current code — which is common on an older unit and is frequently the part people are not expecting. Get two quotes and ask each of them specifically what code work is included, because that is where the difference between quotes usually lives.
Who to call, honestly
- Replacing or repairing the unit: a plumber. Most places require a licensed plumber for a water heater, gas work is not a general-handyman job, and doing it badly is a carbon monoxide risk rather than a leak risk. We do not verify anyone's licence — check it with your state board yourself.
- Standing water and the cleanup: a local. Drying out, hauling the old unit, dealing with a soaked floor or ruined boxes. Ordinary work, no licence involved.
- Prevention afterwards: a local. A drip pan and drain, a leak sensor, moving anything valuable off the floor near it. Cheap, quick, and the reason this is not a disaster the second time.
The thing that costs people the most
Not the heater. The floor, the drywall and whatever was stored beside it. A water heater in a finished basement or an upstairs closet is worth fitting a pan and a leak sensor to well before it fails — that is a job of well under an hour and it is the difference between an inconvenient morning and a claim.
Frequently asked questions
Is a leaking water heater an emergency?
Treat it as one until you know otherwise, because a failed tank releases its whole capacity. Turn off the power or gas first, then the cold water supply. If the tank is bulging, or the temperature and pressure relief valve is discharging steam or hot water, leave the area and call a plumber immediately — that is a pressure problem, not a water problem.
Can a leaking water heater be repaired?
It depends where it is leaking. Fittings at the top, the relief valve and the drain valve are all repairable. A leak from underneath the tank means the tank has corroded through, and tanks cannot be repaired once that happens. Dry everything, lay paper towel down, and check again in an hour — water runs downhill, so leaks often appear lower than their source.
How long does a water heater last?
Typically eight to twelve years for a tank unit. The manufacture date is usually encoded in the serial number on the label. Past about ten years, a several-hundred-dollar repair buys an unknown amount of time on something that is going to fail anyway.
Do I need a licensed plumber to replace a water heater?
In most places, yes, and gas units are not a general-handyman job in any case — a bad installation is a carbon monoxide risk. We do not verify licences on this platform, so check any licence claim directly with your state licensing board.