Arsenic in Well Water: Where It Comes From and How to Remove It

On this page

1. Where it comes from
2. How common is it?
3. The limit: 10 µg/L
4. Testing
5. Treatment options
6. Paying for treatment
7. Uranium often comes along
8. Sources

Where it comes from

In most private wells, arsenic comes from natural deposits in rock and sediment. EPA also lists runoff from orchards and glass and electronics production wastes (EPA). You can’t see, smell or taste it, and two wells on the same road can test very differently.

How common is it?

USGS estimates that about 2.1 million people in the lower 48 states may use domestic wells with arsenic above 10 µg/L. That’s about 4.8% of domestic-well users, with a range of roughly 1.5 to 2.9 million (USGS). It’s a modeled estimate, not a count of tested wells. The only way to know about yours is to test it.

The limit: 10 µg/L

EPA’s maximum contaminant level for arsenic is 0.010 mg/L (10 µg/L, or 10 ppb), and the health goal is zero. EPA lists the potential long-term health effects above the limit as skin damage, circulatory problems and an increased risk of cancer (EPA).

Watch the units: 0.010 mg/L = 10 µg/L = 10 ppb. How to Read Your Well Water Test Results (MCLs, ppm and ppb Explained)

Testing

• Use a state-certified lab. CDC lists arsenic among the chemicals to ask your health department about. Find labs through EPA’s directory.
• If you plan to treat it, ask the lab or a treatment professional whether you need to know the arsenic type. Minnesota’s health department explains that groundwater can contain arsenic III and arsenic V, and that adding pre-oxidation to treatment ensures both types are reduced.
• After shock chlorination, retest. UGA Extension notes that shock chlorination may temporarily raise arsenic in some areas and recommends testing for arsenic afterward.

Mail-in option covering metals: Tap Score: Essential well water test → (the company lists 25 heavy metals in this kit).

Treatment options

From the Minnesota Department of Health’s comparison of point-of-use (one tap) and point-of-entry (whole-house) units:

Key rules from MDH:

1. Choose a unit certified for arsenic reduction by NSF, UL or the Water Quality Association.
2. Maintain it as the manufacturer directs.
3. Retest the treated water after installation to make sure it works.

The Ohio Department of Health gives similar guidance.

RO options to compare. Confirm each model’s arsenic certification (and whether it requires chlorinated or pre-oxidized water) in NSF’s listings before buying: SpringWell: reverse osmosis systems → · iSpring: RO systems → · Aquasana: RO systems → · Express Water: RO systems →

Whole-house arsenic systems vary widely. Get your test results reviewed by a water treatment professional before you buy. Minnesota points to the Water Quality Association’s provider search.

Paying for treatment

MDH lists possible help: USDA Rural Development Single Family Housing Repair Loans and Grants for eligible low-income homeowners and seniors, plus some state loan programs. Ask your health department what’s available where you live.

Uranium often comes along

Uranium is another natural contaminant tested on many metals panels. EPA’s limit is 30 µg/L (EPA). Connecticut’s public health department names reverse osmosis and ion exchange as two common treatments. It recommends treatment at confirmed levels of 30 µg/L or higher and a retest whenever a result is above 10 µg/L, since levels can vary by season. Both methods require maintenance and periodic testing of the treated water.