How-To · Last updated August 1, 2026
A water heater rarely fails without warning. The signs are usually there for weeks — pooling water, rust streaks, a popping sound — before a slow leak becomes a flooded utility closet.
Rust showing up in your hot water, or streaks running down the outside of the tank — either one points to corrosion happening inside. That's the tank itself failing, not a fitting or a valve.
Even a small amount of water collecting under or around the tank is worth checking. Dry the spot, wait an hour, look again. Comes back? Something's actively leaking.
That popping noise is sediment sitting at the bottom of the tank, and it's not a leak by itself — but it wears the tank down faster and often shows up right before one starts.
Most tank water heaters last 8 to 12 years. Past the decade mark, tank corrosion becomes the most likely explanation for almost any symptom on this list.
Where the water's coming from actually narrows down what's wrong, and it's worth checking before you call anyone.
Usually points to the inlet or outlet fittings where the cold and hot water lines connect, or a failing temperature-and-pressure (T&P) relief valve on top of the tank. Both are often repairable without replacing the whole unit — a loose fitting can sometimes just need re-tightening, though a failing T&P valve should be replaced, not ignored, since it's a safety component.
More often means trouble. This can be the drain valve (sometimes fixable) or, more seriously, corrosion inside the tank itself that's let go — which means replacement, not repair. Water pooling under the tank with no clear source at the fittings above it is the classic sign the tank itself is failing.
A water leak on its own isn't usually an immediate safety emergency — but a gas water heater adds a separate risk worth understanding clearly. The water leak and a gas leak are two different problems that can coincidentally show up around the same unit, and it's important not to assume one explains the other.
Signs of a possible gas issue — a sulfur or rotten-egg smell, a hissing sound near the gas line, or a pilot light that won't stay lit — are not something to investigate yourself. If you smell gas, leave the house and call your gas utility's emergency line from outside, before doing anything else, including flipping light switches. A water leak alone, without any gas smell or hissing, is not a carbon-monoxide or gas-leak emergency by itself — but if there's any doubt, treat it as one rather than guessing.
Nobody checks the water heater closet daily — which is exactly why a slow leak in there can run for weeks before the smell or the stain gives it away. That makes it one of the highest-value spots in the house for a point sensor. See our leak detector guide for options that alert your phone the moment water touches the floor.
FAQ
A small amount of condensation can be normal, but any leak from the tank body itself means it's failing and should be shut off, not kept in use.
Typically 8 to 12 years. Past 10 years, corrosion becomes the most likely explanation for a new leak.
Yes — shutting off the cold water supply and power or gas is a safe first step that limits damage while you wait.
It does — top usually means fittings or the pressure relief valve, often repairable. Bottom more often means internal tank corrosion, which means replacement.
A water leak alone usually isn't a gas emergency, but any sulfur smell or hissing near the gas line is a different problem — leave the house and call your gas utility, don't investigate it yourself.