Well Water Smells Like Rotten Eggs (Sulfur)? Causes & Fixes
A rotten-egg smell is usually hydrogen sulfide gas. It can come from the groundwater itself, from sulfur bacteria in the well or plumbing, or from your water heater.
Step 1: Hot only, or hot and cold?
- Only hot water smells: the water heater is the likely cause. A magnesium anode rod can react with sulfate in the water and produce hydrogen sulfide. Penn State Extension notes that replacing it with an aluminum or aluminum/zinc anode can reduce the odor. Have a plumber do it, and don't just remove the anode, because that can shorten the tank's life and may void the warranty.
- Hot and cold both smell: the source is likely the well, groundwater or treatment equipment.
Step 2: Test the water
Hydrogen sulfide is mostly a nuisance, but the Minnesota Department of Health notes that sulfur bacteria and odors can come with other water quality problems. Test for coliform bacteria and nitrate at a minimum (in Iowa this can be free through your county).
Treatment options
Depending on the cause, options include shock chlorinating the well for bacteria, or treatment equipment such as aeration, oxidizing filters or continuous chlorination for hydrogen sulfide in the groundwater. Get the water tested first so you buy the right system.
Try our well water smell diagnosis tool.
Frequently asked questions
Is rotten egg smell in well water dangerous?
At typical household levels hydrogen sulfide is mostly a nuisance, but the smell can mean bacteria are present. Test your water.
Why does only my hot water smell like sulfur?
Usually the water heater's magnesium anode rod reacting with sulfate. A plumber can swap in an aluminum or aluminum/zinc anode.
Sources
- Penn State Extension: Hydrogen Sulfide (Rotten Egg Odor) in Water Wells
- Minnesota Dept. of Health: Hydrogen Sulfide and Sulfur Bacteria in Well Water
Last checked: October 21, 2026