Well Water Smells Like Rotten Eggs: Causes and Fixes
A rotten-egg smell from the tap is hydrogen sulfide gas. Penn State Extension notes most people can smell it well below 0.5 mg/L, long before it reaches levels that cause health concerns, so it's usually a nuisance rather than an emergency. It can come from the groundwater itself, from sulfur bacteria in the well, or from the water heater.
The first check is free: run the cold tap, then the hot tap. If only the hot water smells, the water heater's magnesium anode rod is the usual cause. If both smell, the source is the well or the water, and a lab test tells you which treatment fits.
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What to do in the first 5 minutes
- Smell the cold water and the hot water separately, at a tap that's been running for a minute.
- If only the hot water smells, have a plumber or the heater's manufacturer advise on replacing the magnesium anode rod with an aluminum or powered one.
- If both smell, collect a sample for a certified lab: ask for hydrogen sulfide, sulfate, iron and coliform bacteria.
- If the smell started suddenly or the water also changed color or taste, test for bacteria before drinking it.
- Have a licensed well contractor or treatment pro size a fix from the lab results, not from the smell alone.
Do not do this
- Don't remove a water heater's anode rod without manufacturer guidance; it can void the warranty and shorten the tank's life.
- Hydrogen sulfide gas is flammable and poisonous in confined spaces; ventilate a well pit or basement where the smell is strong.
- Don't pour bleach into the well without following measured shock-chlorination steps; too much chlorine damages pumps and can make water unsafe.
- Sulfur water corrodes copper and steel; have plumbing and fixtures checked if the smell is long-standing.
What's likely going on
Water heater anode rod
Penn State Extension explains that the magnesium rod in a water heater can turn naturally occurring sulfate into hydrogen sulfide. The tell: only the hot water smells.
Sulfur bacteria in the well or plumbing
Sulfate-reducing bacteria produce hydrogen sulfide. Shock chlorination is the common first step and helps reduce the odor, though it may come back.
Hydrogen sulfide in the groundwater
Some aquifers carry the gas naturally, often in deeper wells or in shale and coal-bearing rock. This calls for whole-house treatment.
A water softener that needs service
A softener that isn't regenerating or sanitized on schedule can harbor bacteria that add to the smell.
Diagnose it now
What it typically costs
The hot-water check costs nothing. Fixes depend on the lab result: Penn State Extension says activated carbon may work below about 1.0 mg/L of hydrogen sulfide, while higher levels call for oxidation (chlorine or potassium permanganate feed with filtration), aeration or catalytic carbon. Get a written quote tied to your test results.
Frequently Asked Questions
Is it safe to drink well water that smells like rotten eggs?
Hydrogen sulfide is usually a taste and odor problem at the levels people notice, but a sudden smell can also mean bacteria. Test for coliform bacteria before drinking, and use bottled water until you know.
Why does only my hot water smell like sulfur?
The water heater is the likely source. Its magnesium anode rod can react with sulfate in the water to make hydrogen sulfide. Replacing it with an aluminum or powered anode often fixes it.
Will shock chlorination get rid of the rotten egg smell?
It helps when sulfur bacteria are the cause, and it's a common first step. If the gas is in the groundwater itself, the smell returns and you'll need continuous treatment.
What treatment removes hydrogen sulfide from well water?
It depends on the concentration. Activated carbon can handle low levels; higher levels usually need oxidation with filtration, aeration or catalytic carbon. A lab test decides it.
The service that handles this
Guidance only — independent local providers assess and price their own work. Last reviewed: October 17, 2026.
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