Take a breath, then work in order
A leaking water heater feels like an emergency, and sometimes it is. But the right response is a handful of calm steps in a sensible order, and most of the damage is avoided by the first two. Here's the sequence.
Five minutes of prep that saves a bad night
The best time to learn where the valves are is when nothing is wrong. Take five minutes this week and do the following:
- Find the cold-water shut-off on the heater, and turn it a quarter-turn to be sure it moves, then open it again.
- Find the main water shut-off for the house and do the same. A valve that hasn't moved in years can stick, and it's better to find out on a calm afternoon.
- Find the gas valve on a gas heater, or the breaker for an electric one. Label the breaker if it isn't.
- Take a photo of the heater's label and keep it on your phone.
- Put a towel and a bucket where you can reach them.
None of that fixes anything. It means that when something does go wrong, you're doing a three-step routine, not hunting for a valve in the dark.
1. Keep yourself safe
Water and electricity are a bad mix. If there's water on the floor around the heater and you need to cross it, or if the heater is electric and the breaker panel is in a wet area, don't wade in. Switch off the power only if you can reach the panel while dry. If you can't, call a plumber or an electrician and stay out of the water.
If you smell gas, leave the house at once. Don't switch lights on or off. Call your gas utility or 911 from outside. This is rare with a water leak, but it's the one rule with no exceptions.
2. Stop the water
Find the cold-water valve on the pipe going into the top of the heater. Turn it clockwise to close it. A lever handle closes when it's at right angles to the pipe. That stops fresh water filling the tank. The water already in the tank will drain through the leak or sit there, but the flow stops.
If you can't find that valve or it won't turn, go to the main shut-off for the house. It's usually by the water meter, at the front of the property, or where the line enters the house. Learn where it is before you need it.
Then open a hot tap somewhere in the house, ideally a high one. It lets air in and eases the pressure, which slows the drip.
3. Stop the heat
For an electric heater, turn off its breaker. An electric element running with no water around it can burn out. For a gas heater, turn the gas control knob to off, or set it to pilot. There's also a gas shut-off valve on the line just before the heater, a quarter-turn valve: handle across the pipe means closed.
If the tank is leaking and the water is hot, be careful. It can scald.
4. Work out where it's coming from
Not every leak means the tank has failed. A few different things look alike:
- Water at the base that seems to be coming from underneath: usually the tank itself, which has corroded through. That's the one that means replacement.
- A drip from the pipe connections on top: loose fittings or a failed connector, which can often be fixed.
- Water running from the relief valve or its discharge pipe: the heater is running at too high a pressure or temperature, or the expansion tank has failed. It's a smaller repair, and the post on expansion tanks explains it.
- Damp that seems to appear after a hot shower and then dries: condensation, particularly on a gas heater, and not a leak.
- Water dripping from the drain valve at the bottom: the valve is worn, and can be replaced.
A tank that is leaking from the body can't be repaired. Once the steel has gone, it's time for a new one.
Drying out and what comes next
Water that's left in a house causes a second problem after the first. Wet drywall, insulation and flooring can start to grow mold within a day or two, so drying matters. Get the standing water up quickly, run fans and open windows, and if the floor or wall is wet through, call a restoration company to dry it properly. Take the photos before you start.
Don't forget the part of the house the water went to. An attic leak usually runs down through a ceiling and into whatever is below it, and the damp can hide behind paint for days. Look at ceilings and walls over the next week for stains or bubbling.
5. Limit the damage
Move anything stored near the heater out of the way. Soak up the water with towels or a wet vacuum, and keep it from spreading. Open a window or a door, and run a fan, so the area can dry. If water has reached a ceiling below an attic heater, move furniture out and put a bucket under any dripping spot.
Take photos of the water, the heater and any damage before you clean up. If the water has reached walls, floors or ceilings, get in touch with your homeowner's policy provider about the damage, because they usually need a record of it.
What a slow leak looks like
Not every leak is a flood. A slow drip from a connector or the relief valve can go on for weeks, leaving a rust ring on the floor or a patch of damp that dries before you see it. Put a dry paper towel under the suspect fitting overnight. If it's wet in the morning, you've found it.
A slow leak is a good problem because it gives you time. It's also easy to ignore, and a dripping fitting can become a failed one. Treat it as a small job to book, not a thing to watch.
6. Call a plumber
Give the age, size and fuel of the old heater, say where it sits, and tell them what you've found and what you've shut off. A like-for-like tank can often be swapped the same day when the unit is in stock, which is why it helps to have read the label in advance. The post on reading a water heater's label shows how, and the same-day installation page explains what can and can't be done quickly.
A swap that needs more, such as a move from the attic, a change of fuel or a bigger gas line, is scheduled after the fit check. That's quicker to explain on the phone than it sounds.
Why a tank leaks from the bottom
Most leaks from the base of a tank have the same cause. The glass lining inside the steel develops tiny flaws over time, and the anode rod, which is supposed to protect the steel, is used up. Water gets to the steel at the flaw and corrodes it. Sediment on the bottom speeds that up, since it holds heat and moisture against the steel where nobody can see it.
Eventually the corrosion eats through, and water seeps out between the steel and the insulation, then pools at the base. It starts as a damp patch and can grow into a steady drip. By the time you see water, the damage has been going on for a long while.
That's why a leak from the body isn't repairable. There's no way to patch the inside of a steel tank. It's also why the date on the label matters, because a tank at the end of its life is the usual suspect when water turns up at the bottom.
After the new heater goes in
This is the moment to fix what let the leak do harm. If the heater sits above a living space, ask for a drain pan with a drain line, so the next leak runs to a safe place instead of down the wall. If the system is closed, ask about an expansion tank. If the drain valve was stiff, ask for one you can reach. These are small jobs next to a flooded ceiling, and they're listed as lines on the quote. The replacement page shows where they fit.
And if the old heater was in the attic, think about whether it should go back there. The post on where a water heater should go covers the choices.
A short note on what a plumber will ask
When you call, expect a handful of questions, and having the answers ready speeds everything up. Is it gas or electric? How old is the heater, and how big? Where is it? Where is the water coming from? Have you shut the water and the power or gas off? Is anything damaged yet?
If you can send a photo of the heater and the label by text, do. It saves a surprising amount of back and forth, and a good plumber can often tell from the picture which unit to bring.