A puddle under your water heater is one of two things: a small drip from a valve (often a DIY fix or minor repair), or the tank itself leaking (which means the unit needs to go, today). Figuring out which one you have takes about five minutes and a flashlight.
Start Here: Find Where the Water Is Coming From
Dry the floor around the base and watch for 10-15 minutes. Then trace the moisture up.
The three most common sources on a tank-style water heater:
Drain valve (near the bottom of the tank, looks like a hose bib). This is the best-case scenario. The valve wears out over years. You’ll see a slow drip or wet threads around the valve body. If the handle was bumped or turned accidentally, water may be trickling past the valve’s sealing surface.
Temperature and pressure relief valve (TPR valve) (on the side of the tank, usually with a discharge pipe that runs to the floor or outside). This valve is designed to open if pressure or temperature inside the tank gets too high. A small amount of water in the drain tube occasionally is normal, but a steady drip or puddle near the discharge point means either the valve is failing or the system pressure is running too high. Do not ignore this one.
The tank itself. If water is seeping from around the base of the tank, or you see rust-colored water or mineral deposits on the steel shell, the tank liner has failed. This isn’t fixable. A liner failure means water has been working through the steel from the inside, and once it’s breached far enough to leak out, the tank is done.
How to Tell the Difference
Get a flashlight and look carefully:
- Wet around the drain valve threads or the valve body itself: drain valve issue.
- Water in the TPR discharge pipe or a puddle near where that pipe terminates: TPR issue.
- Water forming at the very bottom seam of the tank, or rust staining on the outside of the tank shell: tank failure.
- Condensation: if it’s a new installation or the weather just turned cold and humid, water on the outside of a cold tank is normal and temporary. It usually clears up once the tank heats up, typically within a few hours to a day.
One thing that fools people: water can run down from a valve and pool at the base, making it look like the tank is leaking. That’s why you wipe it dry and watch, rather than just glancing at the puddle.
What to Do While You Wait for the Plumber
If you’ve found an active leak, do these three things now:
- Shut the cold water supply valve to the heater. It’s usually directly above or beside the unit.
- Turn the heater off. Gas: set the dial to “pilot.” Electric: trip the breaker.
- Note the age of the unit from the serial number on the label. The plumber will want to know.
That’s the right scope for a homeowner. Drain valve work, TPR inspection, any gas-line or electrical work, and anything that requires draining the tank are jobs for a licensed plumber. Even a drain valve that looks like a simple swap involves working on pressurized plumbing, and getting it wrong turns a small drip into a much bigger mess.
The TPR valve is a safety device. If it’s weeping, something is causing it to open, whether that’s a failing valve, high system pressure, or a missing expansion tank. Replacing it without diagnosing why it’s opening doesn’t fix the problem. A plumber checks incoming pressure and the full system before signing off.
Tank failure is not repairable. Once the liner has given out, the water will find another path. There’s no patch that holds long-term. If water is actively flowing from the base of the tank, shut the supply valve and the heater off now, then call.
A Note on Tank Age
Most residential tank water heaters last 8-12 years, sometimes longer depending on water quality and maintenance. If yours is in that range and leaking, the honest answer is that repair may not be worth it even if it’s just a valve. A plumber can give you a straight opinion on whether a repair makes financial sense given the tank’s age and condition.
The serial number on the label encodes the manufacture date. The format varies by brand, so it’s not always obvious how to read it, but a plumber can tell you the age quickly. There are also free online decoders for most major brands if you want to look it up yourself.
When to Call a Licensed Plumber
Call immediately if:
- Water is coming from the base of the tank or you see rust on the shell.
- The TPR valve is dripping or running.
- You’re not sure where the leak is coming from.
- The tank is more than 10 years old and showing any signs of trouble.
Water heater work in California requires a licensed contractor. You can verify any license at cslb.ca.gov. Don’t let anyone work on it without pulling a permit if one is required, and don’t let an unlicensed handyman replace a gas water heater. It’s not worth the risk on a gas appliance.
This guide helps you understand what you’re looking at before the plumber arrives. A tank leak is not something to manage with towels and a bucket. The water damage from a tank that lets go fully will cost far more than a timely replacement would have. Get a licensed plumber out to diagnose it properly.