A leaking water heater means one of five things, and the location tells you which. Top connections and the drain valve are usually a cheap fix. The relief valve points to a pressure problem for a plumber. Water pooling under the tank means the inner tank has rusted through, and that is a replacement, not a repair.
First, make it safe
Before you hunt for the source, shut things down so you can work around standing water and a hot tank. Do these in order:
- Cut the heat. For an electric heater, flip its breaker off at the panel. For a gas heater, turn the gas control dial to "pilot" or "off." Do not relight anything yet.
- Stop the water. Close the cold-water inlet valve on top of the tank by turning it clockwise. If you can't find it or it won't budge, close the main shutoff for the house.
- Find the true source. Wipe every surface dry with a towel, then watch for one or two minutes. Water travels and drips before it pools, so the first wet spot to return is your real leak, not always where the puddle sits.
If you smell gas at any point, stop. Leave the house, do not touch any switch or phone indoors, and call your gas utility's emergency line from outside or a neighbor's.
Leak location triage
Match the wet spot to the row below. The verdict column is the honest "fix it or replace it" call, not a maybe.
| Leak location | Likely cause | DIY or pro? |
|---|---|---|
| Top, at hot or cold connections | Loose fitting or worn gasket | Often DIY: tighten or replace the fitting |
| Temperature-and-pressure (T&P) relief valve | Worn valve or genuine over-pressure | Pro: this is a safety valve, never cap or block it |
| Drain valve (bottom spigot) | Sediment or a worn plastic valve body | Usually pro: replace the valve, tank is fine |
| Pooling under the tank | Inner steel tank corroded through | Replace: a pressurized tank can't be safely patched |
| Any leak plus a gas smell | Possible gas leak | Leave and call the gas utility from outside |
Top connections: usually the easy one
If the water shows up where the two pipes meet the tank, you've found the lowest-severity leak there is. The fittings loosen over years of heating and cooling, or a gasket inside a flexible connector wears out. The tank itself is fine.
With the power and water already off, try snugging the fitting with a wrench. A quarter turn is often enough; don't crank it. If the connector is corroded or still weeps, swap it for a new braided line. This is the one leak most homeowners can clear in an afternoon. If the leak sits higher up and you're hearing other symptoms, see water heater making popping noise for what sediment does inside the tank.
The T&P relief valve: hands off, call a plumber
The temperature-and-pressure relief valve is a safety device. It opens on purpose when the tank gets too hot or the pressure climbs too high, dumping water down a discharge pipe so the tank can't rupture. A weeping T&P valve means one of two things: the valve is worn out, or the tank is genuinely over-pressurized.
Here's the part people get wrong. A brand-new valve that keeps weeping is not a bad valve; it's a pressure problem. Closed plumbing systems with a check valve or pressure-reducing valve at the meter have nowhere to send expanding hot water, and the fix is usually a thermal expansion tank. That's diagnosis and code work for a plumber. Never cap, plug, or thread a fitting onto a T&P valve to stop the drip. You'd be disabling the one part that keeps the tank from becoming a hazard.
The drain valve: small part, pro swap
The spigot at the bottom is where you'd attach a hose to flush the tank. It weeps when sediment lodges in it or the plastic body cracks with age. The good news: the tank is sound. The catch: replacing it on a full tank is messy, and the threads can seize, so most people hand this to a plumber. Staying on top of how often to flush a water heater keeps sediment from chewing up the drain valve in the first place.
Pooling under the tank: this is a replacement
If you've dried everything, ruled out the connections, the T&P valve, and the drain valve, and water keeps collecting under the tank, the inner steel tank has corroded through. Storage tanks have a glass lining and a sacrificial anode rod to slow rust, but once the steel perforates, water seeps from the bottom seam or floor. A pressurized tank can't be safely patched or welded. Plan on a new unit. Our guide to the cost to replace a water heater walks through what to budget, and water heater leaking from the bottom covers this failure in more detail.
Common questions
Is a leaking water heater an emergency?
A slow drip from a top fitting can wait a day. A steady leak, water near electrical, or any gas smell is urgent. Shut off the power and water, and if you smell gas, leave and call the utility from outside.
Can I just patch the tank?
No. The tank holds pressurized hot water, and a patch or weld can fail under that load. If the leak is the tank body itself, replacement is the only safe answer.
Why does my T&P valve drip after I replaced it?
A new valve that keeps weeping is telling you the system pressure is too high, usually a closed system without an expansion tank. The valve is doing its job. A plumber should test the pressure and add an expansion tank if needed.
How long do water heaters last?
A typical tank lasts 8 to 12 years. If yours is in that range and the leak is from the tank body, repair money is better spent on a replacement.
The water heater leaks but there's no hot water too. Related?
Sometimes. Sediment, a failed element, or a tripped breaker can cause both. See water heater with no hot water to work through the heat side separately.
Good maintenance rhythm
- Monthly: glance under and around the tank for damp spots or mineral crust.
- Yearly: flush the tank to clear sediment and test the T&P valve's discharge.
- Every 3 to 5 years: check the anode rod and replace it if it's mostly gone.
- Ongoing: if the tank is past 10 years, budget for replacement before it fails.