EPA legal limit
No federal limit
Maximum Contaminant Level
EWG health guideline
No guideline
Science-based, stricter target
Health effects
Geosmin is not considered a health hazard at the concentrations found in drinking water. It is an aesthetic contaminant — its significance is taste and odour rather than toxicity. However, its presence can indicate algal blooms in source water, which may co-occur with cyanotoxins that are a health concern.
Where it comes from
Produced by cyanobacteria (blue-green algae) in reservoirs and lakes, and by Streptomyces bacteria in soil. Blooms are more common in warm weather and can cause sudden, strong taste and odour events in surface water utilities.
How it's regulated
No EPA MCL — unregulated. Utilities manage geosmin through treatment processes including activated carbon and ozonation. Seasonal complaints are common in systems drawing from warm-weather reservoirs.
How to filter geosmin
Not all filters address geosmin. Look for independently certified filters—NSF International certification means the removal claim has been independently verified.
Frequently asked questions
What is geosmin?
A naturally occurring organic compound produced by cyanobacteria (blue-green algae) and certain soil bacteria. Responsible for the earthy, musty smell sometimes noticed in tap water — detectable by the human nose at concentrations as low as 0.000005 ppb.
What are the health effects of geosmin?
Geosmin is not considered a health hazard at the concentrations found in drinking water. It is an aesthetic contaminant — its significance is taste and odour rather than toxicity. However, its presence can indicate algal blooms in source water, which may co-occur with cyanotoxins that are a health concern.
Is geosmin regulated in drinking water?
No EPA MCL — unregulated. Utilities manage geosmin through treatment processes including activated carbon and ozonation. Seasonal complaints are common in systems drawing from warm-weather reservoirs.
Where does geosmin come from?
Produced by cyanobacteria (blue-green algae) in reservoirs and lakes, and by Streptomyces bacteria in soil. Blooms are more common in warm weather and can cause sudden, strong taste and odour events in surface water utilities.
How do I remove geosmin from tap water?
The most effective methods for removing geosmin are: Activated carbon block filter, Granular activated carbon (GAC). Look for NSF-certified systems—independent certification confirms removal claims have been verified.
Is geosmin in your water?
Enter your ZIP code to see the measured level in your specific utility.