USA Expert Plumbing

Hot water smells like rotten eggs: causes and fixes

By USA Expert Plumbing Editorial Team. Updated . 2 min read.

Short answer

If only the hot water smells, bacteria in the tank are usually reacting with the magnesium anode rod and producing hydrogen sulfide gas. Flushing the tank and replacing the anode with an aluminum-zinc or powered anode usually fixes it.

In this guide
  1. Hot water only, or cold too?
  2. Why the water heater makes the smell
  3. How to fix it
  4. If the cold water smells too

The smell is hydrogen sulfide, the same gas that gives rotten eggs their odor. At the levels found in household water it is unpleasant rather than dangerous, but it is a sign that something in your water heater needs attention.

The first step is to find out whether the smell comes from the heater or from your water supply.

Hot water only, or cold too?

Run cold water from a faucet and smell it, then do the same with hot water.

What you noticeMost likely source
Only the hot water smellsA reaction inside the water heater
Hot and cold both smellThe water supply, often a well
Only one faucet or drain smellsThat drain or fixture, not the water

Why the water heater makes the smell

Most tanks have a magnesium anode rod that corrodes on purpose to protect the steel tank. Sulfate-reducing bacteria, which are common and harmless in many water supplies, react with that magnesium and give off hydrogen sulfide. Warm water and a tank that sits unused, like after a vacation, make it worse.

How to fix it

Flush the tank

Flushing the tank clears sediment where bacteria live and often reduces the smell for a while. It rarely solves the problem alone.

Replace the anode rod

Swapping the magnesium anode for an aluminum-zinc anode, or for a powered anode that uses a small electrical current, is the most common lasting fix. A powered anode does not react with the bacteria at all.

Do not simply remove the anode rod. Without it the tank corrodes much faster, and most manufacturers void the warranty.

Disinfect the tank

Some manufacturers describe a procedure to kill the bacteria with hydrogen peroxide or chlorine. Follow your heater's manual exactly, since the right product and amount depend on the tank size and type.

Raise the temperature temporarily

Heating the tank to about 140°F for several hours can kill bacteria. This creates a real scald risk, so warn everyone in the house, keep hot taps closed and turn the thermostat back down afterward.

If the cold water smells too

The problem is in your water source. City water customers should call the utility. Well owners should have the water tested; treatment options include shock chlorination, aeration and filtration systems designed for hydrogen sulfide.

Common questions

Is it safe to shower in water that smells like rotten eggs?

At typical household levels, hydrogen sulfide is a nuisance rather than a health risk. If the smell is very strong, or you are on a well, have the water tested.

Why did the smell start after I got back from vacation?

Water that sits warm and still in the tank gives bacteria time to react with the anode. Running the hot water for several minutes often reduces it, but it tends to come back until the anode is changed.

Will a water softener cause a rotten egg smell?

Softened water can speed up anode corrosion, which can make the smell more likely in some homes.

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