Rotten Egg Smell From Hot Water: Causes and Fixes

You turn on the hot water at the kitchen sink and catch a smell like rotten eggs. The cold water smells fine. A rotten egg smell from hot water is one of the more common plumbing complaints we hear about, and the good news is that it usually has a clear cause and a practical fix.

This guide explains where the smell comes from, how to tell whether the water heater or the water supply is the source, what it means when we find it during a home inspection, and the safe ways to get rid of it.

What causes a rotten egg smell from hot water

The smell is hydrogen sulfide gas dissolved in the water. In a water heater, it usually comes from one of two sources, or both working together:

• Sulfur bacteria. Sulfate-reducing bacteria are harmless to people, but they thrive in the warm water inside a tank. As they live and feed, they give off hydrogen sulfide.
• The anode rod. Most tank water heaters have a sacrificial anode rod, usually magnesium, that protects the steel tank from corrosion. Penn State Extension explains that the magnesium rod can chemically reduce sulfates in the water to form hydrogen sulfide. That is why the smell may be noticeable only in the hot water.

Water heater manufacturers describe the same thing. Rheem notes that water with high sulfate or mineral content, combined with the tank’s corrosion protection, can produce a rotten egg odor in the heated water.

The amount of gas it takes is tiny. University of Nebraska-Lincoln Extension says most people can smell as little as 0.5 parts per million, and at 1 to 2 ppm the water smells clearly of rotten eggs.

Is the smell coming from the water heater?

The Minnesota Department of Health suggests a simple test: smell the hot and cold taps separately, ideally after the water has not been used for a few hours.

In homes on treated city water, such as most homes in Fargo, West Fargo and Moorhead, a smell that shows up only in the hot water almost always points to the water heater. Many rural homes across North Dakota and Minnesota rely on private wells, where hydrogen sulfide and sulfur bacteria can also be present in the water itself. If you are on a well and both taps smell, start with a water test.

Also make sure the smell is really in the water and not coming up from the drain: fill a clean glass, step away from the sink and smell the glass.

Is it harmful?

At the levels found in household water, hydrogen sulfide is usually a nuisance rather than a health risk. Penn State Extension notes there is no drinking water standard for it because the smell makes water unpleasant long before it reaches harmful levels, and the sulfur bacteria themselves are not a health concern. UNL Extension adds that higher levels in a small, enclosed shower can cause nausea.

UNL Extension also notes that at 1 to 2 ppm the water is very corrosive, which is hard on plumbing and fixtures over time.

What it means when we find this during an inspection

When we run water during a home inspection, we check the hot and cold taps throughout the home. If the hot water has a foul odor, we note it in the inspection report and recommend having the water heater evaluated by a licensed plumber and the water tested.

The finding is rarely urgent, but it is worth sorting out early so you treat the right cause. If the home has a water softener or a private well, mention it to the plumber, since both can play a part.

You can learn more about what we check in a home buyer’s inspection, or schedule a homeowner inspection if you already own the home.

How to get rid of the smell

Start with the least invasive fix and work up. Check your water heater’s manual first: manufacturers have specific instructions, and some fixes affect the warranty.

• Replace the anode rod. Penn State Extension says replacing the magnesium rod with an aluminum rod should eliminate the odor in many cases. GE Appliances recommends a less-active anode material installed by a plumber. A.O. Smith notes that an odor-reducing anode may reduce but not always eliminate the problem.
• Disinfect the tank. Rheem and GE Appliances both describe chlorinating the water heater and hot water lines to kill the bacteria. A plumber can do this alongside an anode change. The Minnesota Department of Health notes that bleach disinfection may only last a few weeks if the source of the bacteria is not addressed.
• Heat treatment, with care. GE Appliances says raising the tank temperature to 140°F can reduce the odor, and the Minnesota Department of Health describes heating the tank to 160°F for several hours and then flushing it. MDH warns this is dangerous: the relief valve must be checked first, the thermostat must be turned back down afterward, and a plumber should do it unless you are experienced. Hot water at 140°F can cause a severe burn in about 6 seconds, according to the U.S. Consumer Product Safety Commission.
• Check the water softener. UNL Extension notes that softeners can give sulfate-reducing bacteria a place to grow. If the softened water smells and the bypassed water does not, have the softener cleaned and serviced.
• Treat the water at the source. For well water with hydrogen sulfide, NDSU Extension advises that treatment equipment be installed upstream of the water softener. A water test tells you what you are treating before you buy equipment.

One fix to avoid: do not simply remove the anode rod. A.O. Smith and Rheem both warn that running a water heater without an anode voids the warranty, and Rheem notes it greatly shortens the life of the tank.

How to keep it from coming back

• Keep the water heater at a safe setting after any treatment. The CPSC and the U.S. Department of Energy both recommend about 120°F for everyday use.
• Have the anode rod checked. A.O. Smith recommends inspecting the anode every 3 years. A worn or replaced rod is also a good time to switch materials if odor has been a problem.
• Service the water softener on schedule and keep the brine tank clean.
• Test private well water regularly, and retest if the smell changes or spreads to the cold water.

Rotten egg smell from hot water: common questions

Why does only my hot water smell like rotten eggs?

When the cold water is fine, the problem is almost always inside the water heater, where warm water, sulfur bacteria and the anode rod combine to make hydrogen sulfide.

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

At typical household levels it is usually a nuisance, not a health risk. UNL Extension notes that higher levels in a small enclosed shower can cause nausea, so improve ventilation and get the problem fixed rather than living with it.

Does a water softener cause a sulfur smell?

It can contribute. Softeners can host sulfate-reducing bacteria, and Penn State Extension notes that in rare cases adding a softener can lead to hydrogen sulfide production. The tap test above helps tell whether the softener is involved.

Should I test my well water?

Yes, especially if both hot and cold water smell. A test tells you whether hydrogen sulfide, sulfate or other problems are in the water so you can choose the right treatment.

Sources

• Minnesota Department of Health, Why Does My Water Smell Like Rotten Eggs? Hydrogen Sulfide and Sulfur Bacteria in Well Water.
• Swistock, Bryan. Hydrogen Sulfide (Rotten Egg Odor) in Water Wells. Penn State Extension, updated December 2024.
• University of Nebraska-Lincoln Extension, NebGuide G1275, Drinking Water: Sulfur (Sulfate and Hydrogen Sulfide).
• NDSU Extension Water Quality, Rotten egg odor from the raw water tap or directly from the well, and publication WQ1352, What’s Wrong With My Water? Choosing the Right Test.
• Rheem, A.O. Smith and GE Appliances water heater use and care guidance on anode rods and hot water odor.
• U.S. Consumer Product Safety Commission, Tap Water Scalds (Publication 5098).
• U.S. Department of Energy, Energy Saver Guide (2022).