Why Your Hot Water Smells Like Rotten Eggs (and How to Fix It)

Turning on the shower and getting hit with a sulfur smell is unpleasant. The good news is that the cause is usually simple and fixable. If you want it handled for you, our water heater maintenance in Newark covers flushing, tank treatment and anode rod swaps. This guide explains why hot water smells like rotten eggs, how to test where the smell comes from and which fixes last. Before anything else, rule out gas.

First: is it the water or is it gas?

Natural gas has no smell on its own. Gas utilities add an odorant called mercaptan so leaks smell like rotten eggs. So where you notice the smell matters.

If you smell gas, do not flip switches or use anything that could spark. Delmarva Power tells customers to get to a safe place and call 911 or its gas emergency line at 302-454-0317.

Why does my hot water smell like rotten eggs?

The smell is hydrogen sulfide gas. In a water heater, three things combine to make it:

1. Sulfate in the water. Many water supplies carry some.
2. Sulfate-reducing bacteria. These are common and harmless to people.
3. A magnesium anode rod. This rod protects the steel tank from rust. It also gives off electrons that the bacteria use to turn sulfate into hydrogen sulfide.

Warm, still water in the tank makes a good home for the bacteria. That is why the smell shows up only on the hot side. The Minnesota Department of Health's guidance says that if the cold tap has no smell, the problem is likely in the water heater.

Our guide to the water heater anode rod explains how the rod works and how long it lasts.

The hot-and-cold tap test

This two-minute test tells you where to focus:

1. Pick a tap you use often, like the kitchen sink.
2. Run cold water for a minute. Smell it in a clean glass.
3. Run hot water for a minute. Smell it in a second glass.
4. Compare. Hot only means the heater. Both means the supply.
5. Check other taps. If only one bathroom smells, look at that drain.

How to get rid of the rotten egg smell in hot water

Fixes range from quick to permanent. Most homes need a mix of steps 1 through 3.

1. Flush the tank

Draining the tank removes standing water and sediment where bacteria live. It will not fix the cause alone, but it helps every other step work. See how to flush a water heater for the steps.

2. Disinfect the tank

The Minnesota Department of Health lists two ways to kill sulfur bacteria in a water heater:

• Chlorination. A bleach solution is added to the tank, left to sit, then flushed out. Follow the heater maker's steps, because amounts and times vary. The health department notes the smell can return within weeks if some bacteria survive.
• Heat treatment. The department suggests raising the tank to 160°F for several hours, then flushing. This is risky. Scalding water can cause severe burns in seconds, so warn everyone in the house, then turn the setting back down. Many people leave this step to a pro.

3. Replace the anode rod

This is the lasting fix in most homes. Options include:

• Aluminum or aluminum-zinc anode. The health department notes a different metal, such as aluminum, can be installed. Many plumbers use aluminum-zinc rods for odor.
• Powered anode. It protects the tank with a small electric current instead of a metal that wears away. It is a common choice where odor keeps coming back.

Do not just remove the anode. The health department warns that doing so may greatly shorten the heater's life, and makers often say it voids the warranty.

4. Treat the water supply

If both hot and cold water smell, the heater is not the main cause. Well owners may need shock chlorination of the well, an aeration system or a filter. City water customers should call their water provider.

Is the smell dangerous?

At the levels found in household water, the smell is mostly a nuisance. The Minnesota Department of Health says sulfur bacteria are harmless, but hydrogen sulfide gas can be dangerous in high amounts in closed spaces like well pits. It also notes that in rare cases the gas comes from sewage or other pollution. If you are on a well, a test for coliform bacteria and nitrate rules that out.

Hydrogen sulfide can also tarnish silver and stain fixtures black over time.

Hot water heater smell after a softener, vacation or new heater

• New water softener. Softened water can speed up the anode reaction. Many homes see odor start soon after a softener is added.
• After a trip. Still water lets bacteria build up. Run each hot tap for a few minutes when you get home.
• Brand-new heater. New tanks come with fresh magnesium anodes. If the old tank had an aluminum rod, the smell can return.
• Low temperature setting. A cooler tank saves energy but can favor bacteria. A periodic flush helps.

Rotten egg smell in Newark, DE homes

• City water vs. wells. Many Newark-area homes get public water from the City of Newark or a utility such as Artesian. If only the hot water smells, the heater is the place to look.
• Wells outside town. Homes on private wells in rural New Castle County are more likely to have sulfur in both hot and cold water. Testing helps you choose the right fix.
• Gas heaters. Northern Delaware gas customers get gas from Delmarva Power. Any gas smell near the heater is a call to them, not a DIY project.

How to keep the smell from coming back

• Use an anode suited to your water if odor has been a problem.
• Flush the tank once a year.
• Run hot taps after trips before using the shower.
• Keep the temperature near 120°F for daily use. See water heater temperature setting.
• Test well water yearly.

Local note: Well homes around Hockessin and outer Middletown see sulfur odor more often than homes on public water in Wilmington. If both taps smell, start with a water test.

Related reading: If the tank is also making popping sounds, read water heater making noise? If you notice rust with the smell, see signs your water heater is going out.

When should you call a water heater professional?

Call a pro if:

• The smell returns within weeks of a flush and bleach treatment
• You want the anode rod changed but it will not budge
• You are thinking about a high-heat treatment
• The water is rusty or dark, not just smelly
• You smell gas near the heater (call your gas utility or 911 first)

Hot water smells like rotten eggs in Newark? Call (302) 732-0874 for water heater maintenance from Newark Heater Pros.