Hydrogen sulfide in drinking water
Also called rotten egg smell, sulfur.
- Legal limit
- None
- Health goal
- None
Values in parts per million (ppm). Comes from the source.
Contaminant referenceLimits checked Oct. 4, 2026
Where the rules stand
No federal limit. Hydrogen sulfide is not on EPA's primary or secondary standards lists. EPA's secondary odor standard (3 threshold odor number) names a "rotten-egg" smell, but it is not a limit for hydrogen sulfide. Penn State Extension says there is no standard because the smell makes water undrinkable long before it reaches harmful levels.
Where to find your level
EPA’s national data doesn’t carry hydrogen sulfide results for utilities. Your utility’s annual water quality report may list it; on a private well, a lab test will.
What EPA says about health
Penn State Extension calls it an aesthetic problem. The gas is poisonous and flammable, but people smell it well before it causes health concerns. Penn State says most people can smell it well below 0.5 ppm, while UGA Extension says most people smell it at 0.5 ppm or higher. Minnesota's health department says the gas can be harmful in the air at high levels, such as in well pits and basements. It can also corrode plumbing and leave yellow or black stains.
Where it comes from
Most often sulfur-reducing bacteria, which live in low-oxygen groundwater, wells and plumbing, according to Penn State Extension. If only the hot water smells, the water heater's magnesium rod may be making the gas.
What handles it
- NSF/ANSI 42
Claim to look for: Hydrogen Sulfide
WQA listing wording, under NSF/ANSI 42. On Oct. 4, 2026, WQA showed it only on whole-house systems from one maker. NSF's 42 page does not name hydrogen sulfide, and NSF's listing search offers no such claim.
Sources
- National Primary Drinking Water Regulations, U.S. EPA. Checked Oct. 4, 2026.
- Secondary Drinking Water Standards: Guidance for Nuisance Chemicals, U.S. EPA. Checked Oct. 4, 2026.
- Hydrogen Sulfide (Rotten Egg Odor) in Water Wells (updated December 10, 2024), Penn State Extension. Checked Oct. 4, 2026.
- Household Water Treatment Techniques and Devices: Activated Carbon Filtration (Bulletin 1542, reviewed July 2024), University of Georgia Cooperative Extension. Checked Oct. 4, 2026.
- Why Does My Water Smell Like Rotten Eggs? Hydrogen Sulfide and Sulfur Bacteria in Well Water (updated 10/18/2024), Minnesota Department of Health. Checked Oct. 4, 2026.
- NSF/ANSI 42, 53 and 401: Filtration Systems Standards, NSF. Checked Oct. 4, 2026.
- Search for NSF Certified Drinking Water Treatment Units (standards and reduction claims lists), NSF. Checked Oct. 4, 2026.
- Find WQA Certified Products (Gold Seal listings by standard and claim), Water Quality Association. Checked Oct. 4, 2026.