Water Heater Leaking? Causes, First Steps and Water Damage Risks

A water heater leaking from any spot needs the same first steps: turn off its power or gas, close the cold-water shutoff valve on the line feeding it, and move valuables away from the water. Then find where the leak is coming from: drips from fittings at the top, the drain valve or the relief valve can often be repaired, but water seeping from the tank body itself usually means the heater needs replacement, according to manufacturer A.O. Smith's water heater leak guide.

Water heater leaking? Do these steps first

Check for safety hazards. If you smell gas (a rotten-egg odor), do not touch light switches or appliances. Leave the home and call 911 from a safe distance, as the U.S. Pipeline and Hazardous Materials Safety Administration advises for suspected gas leaks, then notify your gas company.
Shut off the energy. For an electric heater, switch off its breaker. For a gas heater, turn the gas control to off or pilot, following the label on the unit. A.O. Smith says to turn off power or gas before any inspection.
Shut off the water. Close the cold-water supply valve, usually on the pipe entering the top of the tank. If that valve will not close, shut off the main water valve to the house.
Stay out of standing water near electricity. The CDC says never to turn power on or off while standing in water, and to call an electrician if you cannot reach the panel safely.
Contain and remove the water. Use towels, a wet/dry vacuum or a pump. Move boxes, rugs and stored items off wet floors.
Take photos of the heater, the leak point and any damage before cleanup. This helps with any insurance claim.
Call a licensed plumber for the heater itself, and plan to dry the surrounding area quickly.

Do not drain or refill the tank, and do not restart it, until you know the cause. A.O. Smith's manuals warn never to operate a water heater unless it is completely full of water, because heating an empty tank can damage the tank and the heating elements.

Where is the water coming from?

Dry everything with a towel, then watch where new water appears. The leak location points to the cause.

Where you see water	Common causes	Usually repairable?
Top of the heater	Loose or corroded inlet or outlet fittings, a failing supply connector, or the relief valve threads	Often, by tightening or replacing fittings
Side, from the relief valve or its discharge pipe	High pressure, high temperature, thermal expansion, or a worn valve	Often, but the cause must be found
Drain valve near the bottom	Valve not fully closed, worn washer, or a failed valve	Usually, by replacing the valve
Bottom or base, with no visible source above	Internal tank corrosion or a crack	Usually not; the heater typically needs replacement
Sweating on the outside of the tank	Condensation	Not a leak

Water heater leak at the top

A.O. Smith says a leak at the top often comes from pipe fittings and connections. Water from a top leak can also run down the side of the jacket and pool at the base, so a bottom puddle does not always mean the tank has failed. Check the top first.

Hot water heater relief valve leak

The temperature and pressure (T&P) relief valve is a safety device that opens to release water if the tank gets too hot or the pressure gets too high. A.O. Smith's technical Bulletin 52 lists the main reasons it leaks:

Thermal expansion. In a closed plumbing system, heated water has nowhere to expand, so pressure rises and the valve weeps or dribbles.
High pressure. When tank pressure reaches the valve's rating, the valve opens slightly to relieve it.
A loose threaded connection, which can be resealed.
A large discharge of hot water, which the bulletin attributes only to a malfunctioning thermostat.

Never cap, plug or block a relief valve or its discharge pipe to stop a leak. Rheem's owner's manual states plainly: do not plug the relief valve outlet. A dripping relief valve is a symptom, and the underlying pressure or temperature problem needs a plumber's diagnosis.

Water heater leak at the drain valve

The drain valve sits near the bottom of the tank and is used for flushing sediment. If it drips after flushing, it may not be fully closed or may have debris in the seat. A.O. Smith says that if a drain valve is not closing properly, replacement is usually the solution.

Water heater leak at the bottom

A.O. Smith calls water from the base "often the first indication of a serious problem." Tanks corrode from the inside over time, and the company says this kind of corrosion cannot be repaired and will eventually require tank replacement. A cracked tank typically means a full replacement as well.

Is it condensation?

A.O. Smith explains that condensation can form when cold water fills the tank and chills its outer surface, and that this usually resolves as the heater warms up. Gas units can also show condensation when the burner fires after sitting idle. If water keeps appearing after the tank is fully heated, treat it as a leak.

Why water heaters leak

Age. The U.S. Department of Energy says most storage water heaters last 10 to 15 years, while tankless units can last more than 20 years. Leaks become more likely toward the end of that range.
Sediment. Minerals settle at the bottom of the tank. DOE recommends draining a quart of water from the tank every three months to remove sediment; follow your own heater's manual for the exact schedule.
Corrosion. Tanks have a sacrificial anode rod that corrodes first to protect the tank. Once it is used up, the tank itself starts to corrode.
Pressure. High household water pressure or thermal expansion stresses the tank, valve and fittings.
Connections. Flexible supply lines and fittings wear out. The Insurance Information Institute recommends checking hoses leading to water heaters every year.

Water damage risks from a leaking water heater

A slow leak can soak a floor for weeks before anyone notices, especially in a garage, closet or basement. A sudden tank failure releases the tank's contents and keeps flowing as long as the supply valve is open.

Location matters. The Insurance Institute for Business & Home Safety (IBHS) flagged water heaters installed in attics and on upper floors as a growing concern, because a failure there can damage everything below (IBHS, State of the Risk: Interior Water Damage, 2024). A.O. Smith's own installation instructions say a heater should be installed so that a tank or connection leak will not damage the structure, and that attic or upper-floor installs need a suitable drain pan.

What to check after a leak:

Flooring: Laminate, vinyl plank and hardwood can swell or trap water underneath.
Drywall and baseboards: Water wicks up walls in closets and utility rooms.
Subfloor and ceiling below, for upstairs heaters.
Mold: The EPA says wet materials dried within 24 to 48 hours usually will not grow mold.

Our signs of water damage guide covers the less obvious clues, and our drying out water damage guide explains how to confirm the area is truly dry. For larger losses, see water damage restoration.

Gas water heater leak or carbon monoxide concerns

A water leak and a gas leak are different emergencies. If you smell gas, leave first and call from outside. Gas and other fuel-burning water heaters also produce carbon monoxide if they malfunction or vent poorly. The U.S. Consumer Product Safety Commission lists water heaters among appliances that can produce CO and recommends CO alarms on every level of the home and outside sleeping areas. CPSC notes early CO poisoning symptoms resemble the flu without a fever. If an alarm sounds or anyone has symptoms, get everyone outside and call 911.

If a gas water heater was sitting in floodwater, do not relight it. Have it inspected by a qualified technician first.

Water heater leak fix: repair or replace?

Factor	Points toward repair	Points toward replacement
Leak location	Fittings, drain valve, relief valve	Tank body or base
Age	Well within the 10 to 15 year typical range	Near or past it
Other problems	None	Rusty water, rumbling, frequent relief-valve discharge
Location risk	Garage on slab with floor drain	Attic, upper floor or finished space

A plumber for a water heater leak can confirm whether a component or the tank has failed. Replacement cost depends on fuel type, tank size, venting, code upgrades such as expansion tanks or drain pans, and access.

Prevent the next leak

Inspect yearly. Rheem's manual says to lift and release the relief valve lever at least once a year to make sure it operates freely, and CPSC recommends annual professional service for fuel-burning heating equipment.
Flush sediment on the schedule in your manual.
Install a water heater leak tray and alarm. A drain pan with a line to a drain catches slow leaks. A water heater leak alarm or automatic shutoff valve can stop flow when sensors get wet. The Insurance Information Institute suggests water leak monitoring and shut-off systems.
Know your shutoff valve and make sure it turns.
Plan replacement before the tank reaches the end of its typical life, especially in an attic or upstairs.

Insurance basics

Standard homeowners policies generally treat sudden, accidental water damage differently from problems caused by neglect. The Insurance Information Institute says policies will not cover damage due to lack of maintenance. Whether the water damage is covered, and whether the heater itself is, depends on your policy, so call your insurer and read our water damage insurance claims guide. The Insurance Information Institute also advises documenting damage and keeping receipts for any temporary repairs.

If the leak soaked floors or walls, our what to do after water damage checklist walks through next steps, and you can look up help by area on our locations page. Professional water damage restoration is worth considering when water reached walls, subflooring or a finished room.

Flood Rescue Pros is a free service that connects homeowners with independent local water damage restoration companies. If you would like to be connected with one near you, Get help now.

Frequently asked questions

Is a leaking water heater dangerous?

The water itself is a property risk, but a leak near electrical connections, a gas smell or a CO alarm is a safety emergency. Turn off power or gas, shut off the water, and leave and call 911 if you smell gas.

Can I still use a water heater that is leaking?

It is safer not to. Turn off its power or gas and its water supply until a plumber finds the cause, since manufacturers warn against operating a heater that is not completely full of water.

Where is the water heater drain valve?

It is near the bottom of the tank, usually a faucet-style valve with a hose connection. It is used to flush sediment and to drain the tank for service.

How long do hot water heaters last?

The U.S. Department of Energy says most storage water heaters last 10 to 15 years and tankless units can last more than 20 years. Water quality and maintenance affect the actual life.

How often should I inspect my water heater?

At least once a year, including the relief valve and connections, plus a look around the base whenever you are nearby. Fuel-burning units benefit from annual professional service, which CPSC recommends for fuel-burning heating systems.

Why is my water heater leaking from the bottom?

A bottom leak can be water running down from a top fitting or relief valve, a drain valve that does not seal, or a corroded tank. If the top and valves are dry, the tank has likely failed.

Key facts

First steps: turn off power or gas, close the cold-water supply valve, and contain the water.
Leaks at fittings, the drain valve or the relief valve are often repairable; leaks from the tank body usually mean replacement (A.O. Smith).
A dripping relief valve signals high pressure, high temperature or thermal expansion; never plug it.
Most storage water heaters last 10 to 15 years (U.S. Department of Energy).
Attic and upper-floor water heaters carry higher damage risk (IBHS); use a drain pan and a leak alarm or shutoff.
If you smell gas, leave the home and call 911 from a safe distance, then your gas company.