Arsenic in Well Water: What It Is, Where It's Found, and What to Do About It

arsenic is one of the most common naturally occurring contaminants in private well water in the United States. It has no taste, no smell, and no color. The only way to know if your well water contains arsenic is to test for it.

Where Does Arsenic in Well Water Come From?

Most arsenic in well water is geologic — it occurs naturally in rock and soil and leaches into groundwater over time. It's not a sign of industrial pollution or a spill; it's simply a characteristic of certain aquifers.

Highest-risk states:

• New England (Maine, New Hampshire, Vermont, Massachusetts)
• Western states (Nevada, Arizona, California, Montana, Idaho, Wyoming)
• Great Plains (Nebraska, South Dakota, North Dakota, Iowa)
• Parts of the Upper Midwest (Michigan, Wisconsin, Minnesota)

Industrial sources also contribute in some areas: mining operations, smelters, pesticides manufacturing, and coal combustion sites can elevate arsenic levels in surrounding groundwater.

What Are the Health Risks?

Long-term exposure to arsenic above safe levels is associated with:

• Bladder, kidney, and lung cancer
• Skin conditions (darkening, lesions)
• Cardiovascular disease
• Diabetes
• Neurological effects, particularly in children

The EPA's maximum contaminant level (MCL) for arsenic in public water is 10 micrograms per liter (µg/L), also expressed as 10 parts per billion (ppb). However, there is no truly "safe" level — risk increases continuously with exposure. Some health researchers recommend action at levels above 3–5 µg/L.

Who Should Test?

If you have a private well and live in any of the higher-risk states listed above, you should test for arsenic. It's also worth testing if:

• Your well is deep (deeper wells often have higher arsenic)
• You've never tested before
• You're buying or selling a home

Even if you live outside the highest-risk regions, arsenic can occur in isolated pockets. A one-time baseline test is cheap insurance.

How Much Does Arsenic Testing Cost?

A standalone arsenic test from a find a lab typically costs $15–$40. As part of a broader panel, it's often included at no additional charge. It's one of the cheaper individual contaminant tests.

What to Do If Arsenic Is Found

If your results show arsenic above 10 µg/L (or if you want to treat at lower levels):

Treatment options:

• Reverse osmosis (RO) — Most effective whole-house or point-of-use treatment. Removes 90–99% of arsenic. A quality under-sink RO system costs $150–$500.
• Activated alumina filters — Specifically designed for arsenic removal. Used in whole-house systems.
• Anion exchange — Effective but more complex; typically used in whole-house systems.

Note: standard carbon filters (like Brita pitchers) do not remove arsenic effectively.

After installing treatment, re-test to confirm the system is working as expected.

One Important Note

If arsenic is found in your well, test again in 6–12 months. Natural arsenic levels can fluctuate with water table changes and seasonal patterns. A single elevated result may or may not represent your typical exposure.

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test your well for arsenic with a certified lab. Use our directory to find a lab in your state.