Arsenic in Well Water — Levels, Health Risks & Treatment

Arsenic is tasteless, odorless, and colorless — impossible to detect without testing. Long-term exposure above safe levels is linked to bladder, lung, and skin cancer. In many rural regions, it occurs naturally in groundwater at concerning levels.

Arsenic Levels and Health Risk

Arsenic Level	EPA Status	Health Risk	Action
0–10 μg/L	At or below MCL	Low risk at these levels	Monitor annually
10–50 μg/L	Above EPA limit	Elevated cancer risk with long-term exposure	Treat immediately
50+ μg/L	Significantly elevated	Serious long-term health risk	Do not drink untreated

Where Arsenic Is Most Common

Arsenic occurs naturally in rock formations and dissolves into groundwater in certain geology. It is NOT a sign of industrial contamination in most rural areas — it is simply present in the aquifer. Highest naturally occurring levels are found in:

• Western United States (Nevada, Arizona, California desert regions)
• New England (especially Maine, New Hampshire)
• Upper Midwest (Michigan, Wisconsin, Minnesota)
• Parts of Texas, Oklahoma, and the Great Plains

Treatment Options

Reverse Osmosis — Most Practical

A point-of-use reverse osmosis system removes 90–95% of arsenic from drinking and cooking water. This is the most cost-effective solution for most households. Cost: $200–$500 installed; $50–$100/year in filter replacements. Protects drinking and cooking water but not bath water (not a significant exposure route for arsenic).

Whole-House Arsenic Removal

For households with high arsenic levels or concerns about skin exposure during bathing, a whole-house point-of-entry system using modified activated alumina or iron oxide media can treat all water. Cost: $1,500–$4,000 installed. Requires media replacement every 2–5 years.

Anion Exchange

Similar to a water softener but uses a different resin that targets arsenic. Effective for the arsenate form (As5+) most common in oxygenated groundwater. Less effective for arsenite (As3+) found in some low-oxygen aquifers.

Testing for Arsenic

Home test strips for arsenic are available but have limited accuracy at low levels. For a definitive result, use a certified laboratory. If you are in a high-risk region and have never tested, test now — the EPA recommends all private well owners in elevated-risk areas test for arsenic at least once.