Arsenic in well water
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private wells tested in Norman County, Minnesota had arsenic above the limit, the highest share of any county, according to MDH new private well arsenic tests.
Arsenic occurs naturally in New England bedrock and dissolves into well water. Long-term exposure raises the risk of bladder, lung and skin cancers, and is linked to heart disease and lower IQ in children. It has no taste or smell, so testing is the only way to know.
- EPA limit
- 10 ug/L (EPA MCL (40 CFR 141.62))
- Minnesota level
- 10 ug/L
- CAS number
- 7440-38-2
Check your arsenic number
Type the value from your lab report. It is compared to the EPA limit, the same way the full interpretation does it.
Test your own well for arsenic
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
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Systems that remove arsenic
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Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For arsenic
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For arsenic
Whole-house arsenic and uranium filter
whole-house, at the point of entry, about $2,500
Adsorptive iron-based media; sized to your well yield.
For arsenic
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
Rather have it installed and sized for your well? Book a free in-home water test with a licensed local company.
Where arsenic is worst, by homeowner tests
Counties ranked by the share of private wells above the state guidance level in tests homeowners sent to the state lab. Shares combine town summaries, weighted by wells tested.
| County | Above state level | Wells tested | Highest |
|---|---|---|---|
| Norman County, Minnesota | 178 | ||
| Mahnomen County, Minnesota | 267 | ||
| Strafford County, New Hampshire | 530 | 183 ug/L | |
| McLeod County, Minnesota | 388 | ||
| Clay County, Minnesota | 639 | ||
| Grant County, Minnesota | 254 | ||
| Meeker County, Minnesota | 727 | ||
| Rockingham County, New Hampshire | 2,990 | 766 ug/L | |
| Merrimack County, New Hampshire | 4,603 | 1,040 ug/L | |
| Kandiyohi County, Minnesota | 1,118 | ||
| Stevens County, Minnesota | 204 | ||
| Renville County, Minnesota | 442 | ||
| Faribault County, Minnesota | 138 | ||
| Kennebec County, Maine | 4,743 | ||
| Becker County, Minnesota | 2,435 |
By individual samples
Counties with at least 30 individual samples in public monitoring data, against the EPA limit.
| County | Above EPA limit | Samples | Detected | Median |
|---|---|---|---|---|
| Malheur County, Oregon | 1,112 | 100% | 29.7 ug/L | |
| Kennebec County, Maine | 114 | 99% | 49.4 ug/L | |
| Dawson County, Texas | 72 | 96% | 20.1 ug/L | |
| Churchill County, Nevada | 760 | 98% | 99 ug/L | |
| Terry County, Texas | 52 | 94% | 14.2 ug/L | |
| Reynolds County, Missouri | 54 | 96% | 118 ug/L | |
| Sargent County, North Dakota | 51 | 98% | 20 ug/L | |
| Lapeer County, Michigan | 36 | 92% | 40.5 ug/L | |
| Gaines County, Texas | 57 | 98% | 14 ug/L | |
| De Witt County, Illinois | 92 | 91% | 26 ug/L | |
| Yoakum County, Texas | 63 | 90% | 14.1 ug/L | |
| Macon County, Illinois | 49 | 86% | 21 ug/L | |
| Mono County, California | 458 | 97% | 59.8 ug/L | |
| York County, Maine | 48 | 98% | 55.5 ug/L | |
| Lynn County, Texas | 38 | 95% | 12 ug/L |
How to test
Use a state-certified lab and a proper sampling bottle; hardware-store strips cannot measure arsenic at the levels that matter. Collect from the kitchen tap before any treatment, and again after treatment if you install it.
How to treat
- Point-of-use reverse osmosis
- Adsorptive media (iron-based) whole-house
- Anion exchange
Analysis: Arsenic in private wells, state by state, from the same public records.