Free testing, with limits
Colorado tests private wells for PFAS for free, but not for anything else. Check which tests it includes before you count on it for arsenic.
Colorado's private well pageArsenic in Colorado well water, by county
Arsenic is widespread, over the limit in 15% or more of tested wells, in 2 of the 14 Colorado counties with 10 or more tested wells. 1 more look high, but those results likely overstate it. A county's share tells you how likely a problem is nearby. Only a test of your own well tells you what's in it.
How Colorado compares with the rest of the country
Across Colorado, about 1 in 8 tested wells had arsenic over the EPA limit of 10 µg/L (83 of 697). Across all tested wells in the US it's about 1 in 9. Colorado is about average, so the county you live in tells you more than the state does.
Why it matters: Drinking it for years raises the risk of skin, bladder and lung cancer.
Arsenic dissolves out of certain rocks and old sediments, so it can be high even where nobody has polluted anything.
Arsenic in tested wells, county by county
Share of each county's tested wells with at least one result over the EPA limit of 10 µg/L. Counties need 10 or more tested wells to be listed. Widespread means 15% or more, worth checking 5 to 15%, rare under 5%.
| County | Wells tested | Wells over the limit | Level |
|---|---|---|---|
| Eagle County | 34 | Widespread | |
| Montezuma County | 26 | Widespread | |
| Montrose County | 77 | Widespread | |
| Rio Blanco County | 26 | Worth checking | |
| Lake County | 89 | Worth checking | |
| Elbert County | 30 | Worth checking | |
| Douglas County | 31 | Worth checking | |
| Otero County | 18 | Worth checking | |
| Arapahoe County | 58 | Worth checking | |
| Adams County | 31 | Rare | |
| La Plata County | 55 | Rare | |
| El Paso County | 40 | Rare | |
| Park County | 35 | Rare | |
| Weld County | 22 | Rare |
* Likely overstated. These shares come from a narrow set of wells, so they probably run high for the county as a whole:
- Eagle County: Most of these tests come from one small part of the county, so this likely overstates it.
- Rio Blanco County: All of these tests come from the US Geological Survey, mostly before 2013 in one small part of the county, so this likely overstates it.
30 more Colorado counties have 1 to 9 tested wells for arsenic, too few to rate.
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Where to get your well tested for arsenic in Colorado
A lab Colorado certifies
Ask for arsenic by name. Results from a certified lab count for a home sale or a loan.
Labs certified by ColoradoA mail-in kit
Fill the bottles at your kitchen tap and mail them back. We mark the kits that include arsenic.
Compare kitsKeep reading about wells in Colorado
- Well water testing in Colorado: how to get tested and what turns up statewide
- Arsenic in well water: where it comes from, what it does and how to remove it
- Nitrate in Colorado wells, by county
- Uranium in Colorado wells, by county
- Manganese in Colorado wells, by county
- Lead in Colorado wells, by county
Questions people ask about arsenic in Colorado
Is there arsenic in Colorado well water?
Arsenic is widespread, over the limit in 15% or more of tested wells, in 2 of the 14 Colorado counties with 10 or more tested wells. 1 more look high, but those results likely overstate it. Across Colorado, about 1 in 8 tested wells had arsenic over the EPA limit of 10 µg/L (83 of 697). Across all tested wells in the US it's about 1 in 9. Colorado is about average, so the county you live in tells you more than the state does.
Where can I get my well tested for arsenic in Colorado?
Colorado tests private wells for PFAS for free, but not for anything else. If that doesn't cover you, use a lab certified by Colorado for drinking water, or a mail-in kit that includes arsenic from a certified lab.
See Colorado's list of certified labs, or compare mail-in kits.
Where these numbers come from
- Lab tests: Water Quality Portal (USGS and EPA), well samples since 2000. A well counts as over if any of its tests was over the EPA limit of 10 µg/L. Wells tested for studies and monitoring, not a random sample of homes.
- Likely overstated: our own check of who tested the wells, when and where. How we check.
- State programs and links: Department of Public Health and Environment.