Water on the floor around a heater looks the same whether it costs $25 or $3,000 to fix. What decides the bill is where it starts, and gravity makes almost everything look like a bottom leak.
Spend ten minutes finding the source before you call anyone. It turns “my water heater is leaking” into “the drain valve is dripping”, and that is the difference between a service call and a replacement quote.
If there is no water on the floor and the complaint is temperature, you want the no hot water walkthrough instead.
Where the water shows up, and what it usually means
| Where the water is | Likely source | Typical fix |
|---|---|---|
| Spigot at the bottom | Drain valve | $25 to $250 |
| End of the side pipe | T&P valve | $20 to $200 |
| Trail down from the top | Pipe connections | $150 to $400 |
| Lower panel, electric | Element gasket | $200 to $300 |
| Burner area, sizzling | Condensation | Usually nothing |
| Under the base, all else dry | The tank | $880 to $1,830 |
The rest of this guide is how to tell those apart without guessing.
First: shut things down, in this order
If water is running rather than dripping, do this before you diagnose anything.
- Cut the heat. On a gas unit, turn the knob on the gas valve to OFF, not PILOT. On an electric unit, switch off its double-pole breaker.
- Cut the water. Close the cold-water shutoff on the pipe entering the top of the tank. If there is no dedicated shutoff, close the main.
- Leave the tank full for now. A full tank shows you where the water comes from. An empty one hides it, and draining 50 gallons through a garden hose takes half an hour you do not need to spend yet.
Never put the heat back on while the tank is not full. On an electric heater, an element that is powered without water around it burns out in seconds. On a gas heater, firing an empty tank overheats the flue and can crack the glass lining.
Is it actually a leak, or is it condensation?
There are two kinds of condensation, and both get mistaken for a failed tank.
The jacket sweats. On a humid day, or right after a long shower refills the tank with cold well water, the outer jacket beads up and drips off its bottom edge. Dry the jacket and the floor with a towel and come back in two hours. Sweat comes back as a film over the whole surface. A leak comes back as a trail from one point.
The burner drips. On a gas heater, burning gas produces water vapor. When the tank is full of cold water, that vapor condenses on the cold flue and drips onto the burner, and you hear it sizzle. Water Heater Rescue, a troubleshooting site run by a water heater specialist, describes this as normal on a cold start, stopping once the tank warms up, and notes that sound heaters are regularly returned because the dripping was mistaken for a leak. If the sizzle stops after the first heating cycle and the floor stays dry, there is nothing to fix.
Then rule out the neighbors. A washing machine hose, a softener drain line, an AC condensate line or a foundation seep can all put water next to the heater. Water travels along slab seams and joists and turns up somewhere it did not start.
Is the drain valve leaking?
The drain valve is the spigot at the very bottom of the tank. It is the most common source of a genuine bottom leak and the cheapest part on the appliance.
Wipe it dry, then run a dry fingertip under the outlet and around the base where it threads into the tank. A finger finds a slow weep faster than your eyes do.
- Wet at the outlet: the valve is not seating, usually because sediment from the tank is stuck in it. Many builder-grade valves have no handle, just a slot: turn it closed firmly with a flat screwdriver. If it still drips, open it briefly to flush the grit out and close it again. A brass hose cap with thread tape on the outlet then stops it for years, and it counts as a permanent fix.
- Wet where it threads into the tank: the threads have loosened or corroded. The valve has to come out, and that means isolating and draining the tank first.
Replacing a drain valve runs from about $25 for the part to about $250 with a plumber, depending on whether the tank has to be drained first.
Is the T&P valve discharging?
The temperature and pressure relief valve sits on the top or upper side of the tank, with a pipe running down the side to just above the floor. That pipe is supposed to end there, so a valve that opens puts water exactly where a tank leak would.
Put a finger inside the end of the discharge pipe. Dry means the T&P is not your leak. Wet means the valve is opening, for one of three reasons:
- The water is overheating. A standard residential T&P opens at 210°F or 150 psi. Water hot enough to reach that means a thermostat or gas control has failed. Shut the heater off and have it checked before you touch the valve.
- The pressure is too high. The plumbing code caps static water pressure in a house at 80 psi (IRC section P2903.3.1). Start above that, add the expansion of water as the tank heats, and a closed system can climb to the valve’s setting on every cycle. A $10 gauge on a hose bib tells you the static pressure in a minute. The cure is a pressure-reducing valve at the service entrance, plus a thermal expansion tank if your system has a check valve or backflow preventer.
- The valve is worn. Old valves seep continuously once the seat is tired. Replacement runs $20 to $200 nationally, per HomeAdvisor’s 2026 data.
Do not lift the test lever on an old T&P to “see if it works”. A valve that has not moved in years often will not reseat, and you will turn a dry valve into a dripping one. And never cap or plug the discharge pipe. That valve is the only thing between a stuck thermostat and a tank that ruptures, and how its pipe must run and end is set by the water heater chapter of the International Residential Code.
Are the connections above the tank leaking?
Run a dry paper towel around the cold inlet and hot outlet on top of the tank, along the flex connectors, and around the base of the T&P valve. A few drops an hour from any of them can run down the outside of the tank, under the jacket, and collect at the bottom with no visible trail.
On tanks past about eight years, dielectric nipples are a frequent culprit. Their plastic lining breaks down, the joint corrodes, and the fitting starts to seep at the threads. Repairs land at $150 to $400, because the water has to be shut off and the joint taken apart.
Electric heater: is the element gasket leaking?
An electric tank has two access panels on its side, each covering a heating element that screws through the tank wall with a rubber gasket. When the lower gasket fails, water runs down inside the jacket and appears at the base, which looks exactly like a tank leak.
Switch off the breaker, remove the lower panel, and fold back the insulation. Rust-colored streaks, mineral crust or wet insulation around the element is your answer. A new gasket, or a new element if the old one is corroded, runs $200 to $400 installed. It is not a beginner job: the tank has to be drained below the element, and the terminals carry 240 volts when the breaker is on.
Is the tank itself rusted through?
Every glass-lined steel tank is on a clock. A sacrificial anode rod corrodes on purpose so the steel does not, and once the rod is used up the tank starts to rust from the inside. Perforation shows up as a weep at a weld seam or at the base.
The quickest check is one plumbers use. With the gas off, remove the outer burner access cover (not the sealed inner door), or the lower panel on an electric heater, and feel the insulation. If the valves and fittings are all dry and the insulation behind the cover is soaked, the tank is leaking from inside the jacket and you have your answer.
The other signs that it is the tank and not a fitting:
- Water reappears at one spot under the bottom edge, and everything above is bone dry.
- Rusty or brown-tinged water in the puddle or from the hot taps.
- The unit is 10 years or older. ENERGY STAR’s own savings math assumes a 13-year life for a water heater, and past 10 years tank failure is the default assumption.
- Water keeps coming back after every wipe-down, with no valve dripping.
A perforated tank cannot be repaired. No sealant, weld or epoxy holds on a corroded vessel at full water pressure, and any contractor who offers one is selling you a week. A 40- or 50-gallon replacement runs $880 to $1,830 installed in a straightforward location, and more in an attic or when the venting or fuel type changes. The water heater replacement cost guide breaks that down line by line.
A new water heater leaking from the bottom
A heater that is only days or weeks old is almost never a failed tank. In rough order of likelihood:
- A connection that was not fully tightened. Check the inlet, outlet and gas or electrical fittings first.
- The T&P relieving. A new tank on a closed system with no expansion tank builds pressure every time it heats, and the T&P lets it out. That is a missing expansion tank, not a bad heater.
- Condensation on the first heat-up. A fresh tank full of cold water sweats and drips onto the burner for the first cycle or two.
- A drain valve left cracked open after the installer filled the tank.
If none of those is it, call the installer, not the manufacturer. A leak in the first year is normally their problem to fix.
Tankless heater leaking from the bottom
A tankless unit has no tank to rust through, so a leak at its base is almost always a fitting, the pressure relief valve, or condensate. High-efficiency condensing models produce acidic condensate continuously while they run and need a working drain line, often with a neutralizer. Check that line for a clog or a disconnected fitting before anything else, then call a technician. The heat exchanger is the expensive part.
Water Heater Reset Button: Where It Is, When to Press It (2026) No hot water after the leak is fixed? The reset button is the next thing to check.Before you pay for a new tank
Read the rating plate. The label on the side of the heater gives the model and serial number, and the serial usually encodes the year of manufacture. That tells you the age, and with the model number it tells you the warranty length.
Check the warranty. A tank that leaks inside its warranty period is usually replaced by the manufacturer. Rheem’s standard residential warranty, for example, covers the tank and parts for six years from installation in a single-family home. It applies only to the original owner, it starts from the manufacture date plus 90 days if you cannot prove the installation date, and it does not cover labor, permits or disposal. So a warranty claim does not make the job free, but it can take the heater itself, often the biggest single line on the invoice, off the bill.
Photograph everything before you clean up. Homeowners policies generally treat a sudden leak and a slow one differently. A standard policy excludes wear and tear and mechanical breakdown, so the heater itself is rarely covered. Damage to floors and walls from a sudden failure may be. Call your insurer before you tear anything out.
Repair or replace
Under 8 years old with a valve, fitting or gasket leak: repair, every time. You are spending under $400 on an appliance with half its life left.
Between 8 and 12 years with a valve leak: still repair, but start pricing replacements, and measure the doorway, because the new heater has to come in the same way.
A leak from the tank body at any age, or recurring problems past 12 years: replace. If you are replacing anyway, ask about a heat pump water heater, which costs two to three times as much to buy and far less to run. Do not budget on a federal tax credit any more. The 25C energy efficient home improvement credit was allowed for property placed in service before 31 December 2025 and does not apply to a 2026 installation. State and utility rebates are separate and many are still running.
Check the space before you commit. ENERGY STAR specifies that a heat pump water heater needs an interior spot that stays between 40 and 90°F year round, with about 1,000 cubic feet of air around it. That rules out a lot of tight utility closets where a gas tank is a straight swap.
Stop the next leak from wrecking the floor
Every tank leaks eventually. What it costs you depends on what is under it.
Avoid 
Better 
One more thing worth knowing if your heater sits in a garage: the wood-and-drywall platforms many builders put under them are the worst possible base. A slow leak soaks the plywood top through, the drywall sides come away in pieces, and the water wicks into the wall behind it long before anyone sees it. When the tank is replaced, ask for a steel stand and a pan instead of rebuilding the wooden box.
