EPA legal limit
10 ppb
Maximum Contaminant Level
EWG health guideline
0.004 ppb
Science-based, stricter target
IARC classification
Group 1
Cancer research classification
Health effects
Long-term exposure to arsenic in drinking water is associated with bladder, lung, and skin cancers. Also linked to cardiovascular disease, diabetes, and adverse reproductive outcomes. The EPA MCL of 10 ppb is 2,500× higher than the EWG health guideline of 0.004 ppb.
Where it comes from
Natural geological sources are the primary cause of arsenic in groundwater. Industrial discharge, wood preservatives, pesticides, and mining operations contribute additional arsenic. Highest concentrations in the U.S. are found in the Southwest, Midwest, and parts of New England.
How it's regulated
Regulated at 10 ppb MCL since 2006. The EWG health guideline is based on a one-in-one-million cancer risk. Many utilities comply with the legal limit while exceeding the health-protective threshold.
The EPA vs EWG gap
The legal limit (10 ppb) is 2500× higher than the EWG health guideline (0.004 ppb). Water can be legally compliant while still exceeding the science-based threshold.
How to filter arsenic
Not all filters address arsenic. Look for independently certified filters — NSF International certification means the removal claim has been independently verified.
Frequently asked questions
What is arsenic?
A naturally occurring metalloid found in rock and soil. Arsenic dissolves into groundwater as water moves through arsenic-containing geological formations. Also introduced through industrial and agricultural activities.
What are the health effects of arsenic?
Long-term exposure to arsenic in drinking water is associated with bladder, lung, and skin cancers. Also linked to cardiovascular disease, diabetes, and adverse reproductive outcomes. The EPA MCL of 10 ppb is 2,500× higher than the EWG health guideline of 0.004 ppb.
Is arsenic regulated in drinking water?
Regulated at 10 ppb MCL since 2006. The EWG health guideline is based on a one-in-one-million cancer risk. Many utilities comply with the legal limit while exceeding the health-protective threshold.
Where does arsenic come from?
Natural geological sources are the primary cause of arsenic in groundwater. Industrial discharge, wood preservatives, pesticides, and mining operations contribute additional arsenic. Highest concentrations in the U.S. are found in the Southwest, Midwest, and parts of New England.
How do I remove arsenic from tap water?
The most effective methods for removing arsenic are: Reverse osmosis (RO), NSF 58 certified RO system, Ion exchange resin, Activated carbon block filter. Look for NSF-certified systems — independent certification confirms removal claims have been verified.
Is arsenic in your water?
Enter your ZIP code to see the measured level in your specific utility.