EPA legal limit
2 ppb
Maximum Contaminant Level
EWG health guideline
0.1 ppb
Science-based, stricter target
Health effects
Mercury is a potent neurotoxin. Inorganic mercury primarily affects the kidneys at levels found in drinking water. Organic methylmercury (not typically a drinking water concern) causes the more severe neurological damage associated with fish consumption.
Where it comes from
Industrial discharges from chlor-alkali plants, mining operations, battery manufacturing, and historical industrial contamination. Can also occur naturally from mercury ore deposits.
How it's regulated
EPA MCL: 2 ppb (0.002 mg/L). The EWG health guideline of 0.1 ppb is based on kidney toxicity endpoints — 20× stricter than the federal limit.
The EPA vs EWG gap
The legal limit (2 ppb) is 20× higher than the EWG health guideline (0.1 ppb). Water can be legally compliant while still exceeding the science-based threshold.
How to filter mercury
Not all filters address mercury. Look for independently certified filters — NSF International certification means the removal claim has been independently verified.
Frequently asked questions
What is mercury?
Inorganic mercury contamination in drinking water is relatively rare but occurs near industrial sites, mining operations, and areas with historical mercury use. It differs from methylmercury — the bioaccumulative organic form found in fish — which is not typically a drinking water contaminant.
What are the health effects of mercury?
Mercury is a potent neurotoxin. Inorganic mercury primarily affects the kidneys at levels found in drinking water. Organic methylmercury (not typically a drinking water concern) causes the more severe neurological damage associated with fish consumption.
Is mercury regulated in drinking water?
EPA MCL: 2 ppb (0.002 mg/L). The EWG health guideline of 0.1 ppb is based on kidney toxicity endpoints — 20× stricter than the federal limit.
Where does mercury come from?
Industrial discharges from chlor-alkali plants, mining operations, battery manufacturing, and historical industrial contamination. Can also occur naturally from mercury ore deposits.
How do I remove mercury from tap water?
The most effective methods for removing mercury are: Reverse osmosis (RO), NSF 58 certified RO system, Activated carbon block filter. Look for NSF-certified systems — independent certification confirms removal claims have been verified.
Is mercury in your water?
Enter your ZIP code to see the measured level in your specific utility.