Hot Water Smells Like Rotten Eggs: The Anode Rod

By Ray Bennett · Updated 2 October 2026 · 6 min read · Checked against the sources at the end

Hot Water Smells Like Rotten Eggs: The Anode Rod

Short answer

First work out whether you smell it in the air or only in the water, because those two have nothing in common. In the air with nothing running is gas and means leaving the house. Only from the hot tap while it runs is hydrogen sulphide in the tank, which is unpleasant, harmless to wash in, and curable in an afternoon.

A rotten egg smell gets two completely different responses depending on where you smell it, and getting that wrong is the only genuinely serious thing on this page.

So this starts with one question, answers it in a minute, and only then explains the part that is causing it.

Before you start

What to carry: a clean glass, a screwdriver and a garden hose. Twenty minutes for the test, an afternoon for the cure.

Gas or electric? The smell in the water happens on both, because it comes from the tank rather than from how it is heated. What changes is the risk if you smell it in the air, because only a gas heater has fuel to leak.

Notice when. Only from hot taps, from every tap, or in the air with nothing running at all. Those are three different pages and only one of them is this one.

One of these means leaving the house. Rotten eggs in the air, with no water running. That is the warning smell added to natural gas and propane. Get everybody out, do not touch a light switch and do not use a phone indoors, then call the gas company from outside: the full list of smells that mean leaving.

The heat cure below runs the tank hot enough to scald in seconds. Tell everyone in the house, keep children away from the taps while it is up, and turn it back down to its normal setting the same day. It is a treatment, not a new setting.

Air or water, and it matters enormously

The same smell, two entirely different instructions. This takes a minute and it is the only part of the page that is urgent.

Check 1

The glass test

Stand in the room with nothing running. If you can still smell it, stop reading and use the warning box above.

Run the hot tap, fill a glass, and take it to another room. If it smells in the glass, it is in the water.

Now do the same with the cold. Hot smells and cold does not means the water heater. Both smell means the supply coming into the house, which is usually a well, and that is a water treatment job rather than a heater one.

If the glass smells fine in the other room but the basin smells when you stand over it, the smell is coming up the drain rather than out of the tap. That is a plumbing trap, not a water heater, and it is a surprisingly common mix up.

What is actually making it

The rod is doing exactly what it was fitted to do. In some water, doing that job produces the smell as a side effect.

Every tank has a sacrificial anode rod screwed into the top and hanging down the middle of the water. It is a soft metal, usually magnesium, and it corrodes so that the steel tank does not. Rheem says running a tank without it greatly shortens the tank’s life.

In water containing sulphates, along with bacteria that are harmless to drink, the reaction at that rod produces hydrogen sulphide. That is the rotten egg gas, and it dissolves in the hot water and comes out of the tap with it.

So a smelly tank is usually a healthy anode in unlucky water rather than a failing water heater. It gets worse after the tank has stood unused for a week or two, and it is worse on tanks kept at a low temperature, because the bacteria prefer it cooler.

Getting rid of it

Check 2

Heat it, chlorinate it, then change the rod

Start with heat. Turn the tank up to about 140 degrees and leave it for several hours, then run every hot tap in the house for a few minutes so the hot water reaches the pipes as well. Then turn the thermostat back down to its usual setting, around 120. On a gas heater the dial often has marks rather than numbers, so note where it was before you move it.

If it comes back, chlorinate it. Switch the power or the gas off and shut the cold supply. Drain the tank, add plain unscented household bleach through the anode port or the hot outlet, one gallon for every 25 gallons of tank in A.O. Smith’s procedure, refill, and let it stand a couple of hours. Then run every hot tap until there is no chlorine smell left anywhere. Never mix bleach with anything else, and never leave it sitting in the tank.

Then change the rod. Swapping the magnesium anode for an aluminium and zinc one keeps the tank protected and can cut the smell, though Whirlpool warns a special rod may reduce it rather than end it. It needs a large socket and real leverage, and on an older tank the rod can be seized solid, which is when it becomes a job worth paying for.

Do not simply take the anode out and leave it out. The smell stops and the tank starts rusting from the inside, which takes years off it and usually ends the warranty. It gets suggested online and it is a bad trade.

The other hot water smells

Check 3Free to find

Name it, because they are not all the tank

Musty or earthy. Usually the supply rather than the heater, and on a house with a softener it is often the softener wanting a service.

Metallic, or like coins. Iron in the water, or on an old tank the steel itself beginning to go. If it arrives alongside rusty coloured water, look at the age of the tank.

Plastic or chemical on a brand new heater. Run several tankfuls through it. If it does not fade, ask the installer, and on a heater that is years old it is worth asking about too.

Anything burning, around an electric heater. That is not a water smell at all, it is electrical. Switch it off at the breaker: what a heater doing this is telling you.

The smell arrived with the noise. Sediment on the bottom of a tank grows both, because it traps water underneath and bakes it: how to get it out.

Questions people ask

Is it safe to shower in?

At the levels that come out of a domestic tank, yes. It is genuinely unpleasant rather than genuinely harmful, which is why it is worth fixing but not worth panicking about.

It cleared up and came back a month later.

Heat and bleach kill what is there now and do not change the chemistry. If it keeps returning, the anode swap is the next step, though Whirlpool warns it may reduce the smell rather than end it.

It only smells after we have been away.

That is typical. Standing water in a warm tank with nobody drawing it off is exactly the condition that builds it up, and a few minutes of running every hot tap on the day you get back usually clears it.

We are on a well.

Then the sulphate is very likely coming in with the water, and the tank is only where you notice it. Treating the supply is the real answer, and it fixes the cold taps too.

How often should the anode be checked?

Rheem says once a year. Whirlpool says after three years at the most, then every year, and every year from the start on softened water. It is worth doing at the same time as a flush. A rod worn down to the wire has stopped protecting anything.

Everything smells, hot and cold.

Then it is not the water heater. That is the supply, and no amount of work on the tank will change what is arriving at the house.

Sources: A.O. Smith technical bulletin 23 (chlorination procedure) and residential electric use and care guide 100264218 (water odor, 140°F), Whirlpool Energy Smart use and care guide 318686-001 (anode rod and water odor), and Rheem use and care manual AP23698 (anode rod, gas odorant)