Arsenic in Well Water: Natural Occurrence, Health Risks & Solutions
2026-04-02 · 7 min read · Contaminant Guide
How Arsenic Gets Into Well Water
Arsenic occurs naturally in certain rock formations and dissolves into groundwater. Unlike many contaminants, arsenic contamination is often natural rather than man-made. The western US, New England, and parts of the Midwest have the highest natural arsenic levels.
EPA Standard
The EPA Maximum Contaminant Level (MCL) for arsenic is 10 parts per billion (ppb). Many public health experts argue this should be lower. Long-term exposure to arsenic above 10 ppb increases risks of skin, bladder, and lung cancer.
Most Affected States
States with highest arsenic levels include: Nevada, Arizona, Maine, New Hampshire, and parts of California. However, localized hotspots exist in nearly every state. Test your well regardless of location.
Treatment
Point-of-use reverse osmosis systems effectively remove 95%+ of arsenic. Whole-house treatment options include adsorptive media (iron-based) and oxidation/filtration systems. Costs range from $200 for under-sink RO to $3,000+ for whole-house systems.
Our team analyzes data from EPA SDWIS & USGS to deliver accurate, up-to-date information. All data is verified and cross-referenced with official sources.