Why Is My Water Heater Leaking From the Bottom?

Water under a water heater has several possible sources, and they range from a fitting that needs tightening to a tank that has reached the end of its life. The distinction matters, because one of those can wait until next week and one cannot.

Deal with safety first

Before investigating anything, do these in order.

Turn off the power or the gas. On an electric heater, switch off its breaker at the panel. On a gas heater, turn the gas control to off, or close the gas shut off valve on the supply line. A tank that loses water while still heating can damage the element or the tank.

Do not stand in standing water to reach an electrical panel or an electric heater. If water has pooled around the unit and you cannot get to the breaker without walking through it, stop and get help.

Close the cold water supply. There is normally a valve on the cold inlet pipe at the top of the heater. Closing it stops more water feeding the tank.

Remember the water is hot. A tank holds water at scalding temperature. Do not open a drain valve or a fitting without allowing for that.

If you smell gas, leave. Do not operate switches on your way out, and call your gas utility from outside.

Find out where the water is actually coming from

Water runs downhill, so a puddle at the base tells you very little about the source. A leak from a fitting at the top will run down the outside of the tank and collect at the bottom, looking exactly like a tank failure.

Dry everything completely, including the floor, the base and the whole outside of the tank. Then lay dry paper towel around the base and at each connection, and check back after an hour or two.

Where the paper gets wet first is where to look.

The drain valve

Near the bottom of the tank there is a valve that looks like an outdoor faucet, used for draining the heater. It is a common source and one of the more benign ones.

Plastic drain valves in particular can weep as they age, and one that has been opened for maintenance sometimes does not seat properly afterwards. Because it sits low on the tank, any drip from it lands straight on the floor and looks like a tank leak.

Dry it and watch. A valve weeping from its spout may only need closing properly. One leaking from the body, or from where it enters the tank, is a replacement.

The temperature and pressure relief valve

This is the safety valve, usually on the top or upper side, with a pipe running from it down towards the floor. Water at the bottom of that pipe has come from the valve, not from the tank.

The valve exists to release water if temperature or pressure inside the tank goes too high. If it is discharging, it may be doing exactly its job, which means something else is wrong.

Do not cap, plug or block this pipe. It is the tank’s protection against a genuinely dangerous failure. A relief valve that discharges repeatedly needs investigating rather than silencing.

Connections at the top

The cold inlet and hot outlet fittings at the top are a frequent source, and the one most often misdiagnosed because the water appears at floor level.

Dry both connections and the pipe either side, then check around them after an hour. Corrosion or a mineral crust around a fitting is a good sign it has been weeping for a while. Flexible connectors have a limited life and are a common culprit.

Condensation

Not every puddle is a leak. Cold water entering a warm tank, in a humid space, produces condensation on the outside that runs down and collects at the base.

It is most likely on a new installation, after heavy hot water use, or in a garage during humid weather. The tell is moisture spread evenly over the outside of the tank rather than a trail from one point, and water that stops appearing once the tank has been up to temperature for a while.

On a gas heater, persistent condensation is worth mentioning when you ask for help, because it can also relate to how the unit is venting.

When it is the tank

If every fitting and valve is dry and water is still appearing underneath, the tank itself is the remaining explanation.

A steel tank is protected internally by a glass lining and a sacrificial anode rod. Once the lining is compromised and the anode is spent, the steel corrodes from the inside out. By the time water appears, the corrosion has already gone through.

This is the answer nobody wants, because a corroded tank is not repairable. Welding, sealants and patches do not work on a vessel holding heated water under pressure. The unit needs replacing.

It also tends not to stay a small leak. A seep can become a substantial failure without much warning, which is why a leaking tank is worth acting on rather than watching. Our article on a heater running out of hot water covers the other symptoms that often appear alongside an ageing tank.

How urgent is it?

Treat it as urgent if water is flowing rather than dripping, if it is near electrical equipment or a panel, if the tank sits in an attic or on an upper floor where a failure would run into rooms below, or if the relief valve is discharging repeatedly.

A slow weep from a fitting, with the supply closed and the unit switched off, is usually manageable over a day or two. See emergency plumbing if it is the former.

Useful things to have ready

Whether the heater is gas or electric, roughly how old it is, where the water appears, whether it is constant or only during heating, and the model information from the label on the side.

Knowing where your shut off valves are before you need them makes all of this easier, and our note on shutting your water off covers that. For repairs, see water heater repair, and where the tank has failed, water heater replacement.

Frequently asked questions

Can a leaking water heater be repaired?

It depends entirely on what is leaking. Valves, fittings and connectors are routinely replaced. The tank itself is not repairable once it has corroded through, and patching is not safe on a vessel holding heated water under pressure.

Is a leaking water heater dangerous?

The water itself is hot enough to scald. The greater risks are water reaching electrical equipment, and a tank that fails more completely without much notice. A relief valve discharging repeatedly is also a signal worth taking seriously rather than ignoring.

Should I drain the tank if it is leaking?

Closing the cold supply and switching off the power or gas is usually enough as a holding measure. Draining involves scalding water and is worth leaving to whoever attends, unless the leak is severe and you have been advised to do it.

For plumbing service in Houston, call (877) 563-1074 to connect with an independent plumbing service provider.