A water heater that’s leaking can go from a damp spot to a flooded utility room overnight, so the first move is simple: figure out where it’s coming from. Most leaks I get called for are a loose connection or a valve doing its job — cheap, fixable things. The one that isn’t fixable is a rusted-through tank, and I’ll show you how to tell the difference.
⚠️ Do this first
If water is actively pooling, shut off the water supply to the heater (the valve on the cold line going in, at the top) and cut the power: for an electric unit, flip its breaker; for a gas unit, turn the gas control dial to “Off.” Don’t ignore a leak hoping it’s minor — a tank under pressure can fail fast. If you’re not sure how to isolate it, my guide to shutting off your water main covers the whole-house shutoff too.
Find the leak by location
Dry everything off, lay down paper towel, and watch for a few minutes. Where the water shows up tells you almost everything:
| Where it’s leaking | Most likely cause | Can you fix it? |
|---|---|---|
| Top of the tank (cold/hot pipe connections) | Loose or corroded fitting on the supply lines | Yes — tighten or replace the connection |
| A pipe running off the side/bottom (the discharge tube) | The T&P (temperature & pressure) relief valve is releasing — often high pressure or a bad valve | Sometimes — see below |
| The drain valve near the floor | Valve not fully closed or worn | Yes — close it or cap it |
| The base of the tank itself | The inner tank has rusted through | No — the heater needs replacing |
The T&P valve: a leak that might be a warning
That valve and the pipe pointing at the floor are a safety device — they dump water if the tank gets too hot or too pressurized. If it’s dripping, you may have water pressure over 80 psi (a $10 gauge tells you), a failing expansion tank, or the temperature set too high. If the valve drips even after you’ve ruled those out, the valve itself is cheap to replace — but never plug it. It’s the part that keeps a water heater from becoming dangerous.
The one leak you can’t fix: a rusted tank
If the water is coming from the bottom of the tank and there’s no connection or valve above it that’s wet, the steel tank has corroded from the inside out. There’s no patch, no sealant, no weld that’s worth doing — once a tank leaks, it’s done. The fix is replacement. If your unit is more than 8–12 years old, this is the most common cause, and it’s a sign the anode rod gave out years ago. Here’s how to replace a water heater step by step, and my picks for the best water heaters if you’re shopping.
Leaks you can usually fix yourself
A weep at the cold or hot connection on top is often just a fitting that backed off — snug it with a wrench, and if it still weeps, redo the joint with fresh tape or a new flex connector. A drip at the drain valve usually means it didn’t seat after a flush; close it firmly, and if it still drips, a brass hose cap screwed onto the outlet stops it for a couple dollars. While you’re there, it’s worth knowing how to troubleshoot a unit that isn’t heating too — the same access panel covers both.
What it costs — and the repair-or-replace call
A valve or connection fix is a few dollars in parts. A leaking tank is a full replacement. Before you decide, it’s worth seeing real numbers: my breakdowns of water heater repair cost and the cost to replace a water heater lay out what’s fair. My rule: fix connections and valves; replace the unit the moment the tank itself leaks or if it’s near the end of its life.
Frequently asked questions
Is a leaking water heater an emergency? It can become one. A small drip from a connection isn’t urgent, but a leak from the tank body can fail suddenly and flood the area. Shut off the water and power to the heater and address it the same day.
Why is my water heater leaking from the bottom? Usually the inner tank has rusted through, which can’t be repaired — the heater needs replacing. Less often it’s the drain valve above the floor not sealing, which is an easy fix.
Can I still use a leaking water heater? If it’s just a dripping connection or drain valve, briefly yes, until you fix it. If the tank itself is leaking, turn it off and stop using it — it will only get worse and can fail without warning.
How long do water heaters last? A typical tank water heater lasts 8–12 years. If yours is in that range and the tank is leaking, replacement is almost always the right call rather than repair.
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