EPA legal limit
50 ppb
Maximum Contaminant Level
EWG health guideline
30 ppb
Science-based, stricter target
Health effects
Chronic selenium exposure above the EPA MCL causes selenosis — hair loss, nail brittleness, and neurological effects. Essential as a nutrient at trace dietary levels; the margin between beneficial and toxic exposure is narrower than most minerals.
Where it comes from
Natural dissolution from seleniferous rocks and soils (common in the western US). Irrigation drainage from agricultural areas can concentrate selenium in downstream water. Coal fly ash impoundments are also a contamination source.
How it's regulated
EPA MCL: 50 ppb. The EWG health guideline of 30 ppb reflects the narrow margin between dietary need and toxicity at chronic exposure.
How to filter selenium
Not all filters address selenium. Look for independently certified filters—NSF International certification means the removal claim has been independently verified.
Frequently asked questions
What is selenium?
Selenium is a naturally occurring trace mineral that is essential in small amounts but toxic at higher levels. In water, it occurs naturally from selenium-bearing rocks and soils, and from irrigation drainage in western US agricultural areas.
What are the health effects of selenium?
Chronic selenium exposure above the EPA MCL causes selenosis — hair loss, nail brittleness, and neurological effects. Essential as a nutrient at trace dietary levels; the margin between beneficial and toxic exposure is narrower than most minerals.
Is selenium regulated in drinking water?
EPA MCL: 50 ppb. The EWG health guideline of 30 ppb reflects the narrow margin between dietary need and toxicity at chronic exposure.
Where does selenium come from?
Natural dissolution from seleniferous rocks and soils (common in the western US). Irrigation drainage from agricultural areas can concentrate selenium in downstream water. Coal fly ash impoundments are also a contamination source.
How do I remove selenium from tap water?
The most effective methods for removing selenium are: Reverse osmosis (RO), NSF 58 certified RO system. Look for NSF-certified systems—independent certification confirms removal claims have been verified.
Is selenium in your water?
Enter your ZIP code to see the measured level in your specific utility.