Hydrogen Sulfide
H₂S·Affects lungs, skin,
The rotten-egg smell in well water. Produced by sulfur-reducing bacteria and geological sulfur deposits. Not acutely toxic at typical home levels but corrosive to plumbing and unpleasant.
H₂S
EPA limit
No federal MCL (taste + odor threshold ~0.05 mg/L)
Most at risk
Well-water households, homes near oil or coal deposits
Found in
Well water
AquaOx filters
YesCatalytic carbon (AquaOx RE Edition)
What it does to you
Health effects
At the concentrations typically found in residential well water (under 1 mg/L), hydrogen sulfide is not considered an acute health hazard for drinking or showering. The EPA has not set a federal MCL because the gas is detectable by smell at concentrations far below any toxicological threshold.
The practical problems are quality-of-life and equipment. The rotten-egg odor makes water unpleasant to drink, cook with, or shower in. Sulfur water can stain bathroom fixtures black, tarnish silverware, and react with iron in plumbing to form black sediment. People with sensitive skin sometimes report mild irritation after extended exposure.
At very high concentrations (well above what's found in drinking water), hydrogen sulfide is genuinely toxic, which is why it's regulated as a workplace hazard in confined spaces. In confined bathrooms with poorly ventilated showers, sustained high-sulfur water can cause headaches and nausea.
Where it comes from
How it gets into your water
Hydrogen sulfide in well water comes from two main sources. First, sulfur-reducing bacteria living in groundwater, well casings, and water heaters consume sulfate and produce H2S as a metabolic byproduct. These bacteria thrive in oxygen-poor environments, which is exactly what most well systems are.
Second, geological dissolution. Wells drilled into shale, sandstone, coal seams, peat deposits, or near oil and gas formations encounter naturally occurring sulfur compounds that release H2S into the water.
A specific scenario worth knowing: water heaters with magnesium anode rods can accelerate sulfur-bacteria activity, which is why many homes only smell sulfur from the hot tap, not the cold.
Sulfur-bearing geology
Shale, coal, oil + gas regions
Sulfur-reducing bacteria
Thrive in oxygen-poor groundwater
Water heater anode rod
Magnesium rods accelerate bacteria
Well casing biofilm
Bacteria colonize the well structure
Find out for yourself
Is it in your water?
Hydrogen sulfide is the easiest contaminant to detect: if your water smells like rotten eggs, sulfur, or a struck match, you have it. The smell threshold is about 0.05 mg/L, well below any health concern level. A water test will quantify the concentration if you want a precise number for sizing treatment.
Municipal water rarely has H2S because chlorination eliminates the bacteria and the gas oxidizes during treatment. This is almost exclusively a private-well issue.
The fix
How AquaOx filters it
Hydrogen sulfide is the specific contaminant the AquaOx RE Edition was built for. The catalytic carbon media in the RE catalyzes the oxidation of H2S into harmless sulfate ions, filtering both the gas and the odor.
The standard AquaOx with Centaur catalytic carbon also handles moderate H2S levels. For homes with severe sulfur problems (strong rotten-egg smell from every tap, visible black staining), the RE Edition is the right call because it's tuned specifically for sulfur chemistry and lasts longer under heavy H2S loading.
Iron-bacteria contamination often goes hand-in-hand with sulfur-bacteria contamination. If your well has both, you may need shock chlorination first to kill the bacteria, then the AquaOx RE for ongoing treatment.
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