Is there arsenic in Colorado drinking water?

In some places, yes, and it's natural rather than dumped there. USGS research and NPR reporting point to elevated arsenic in parts of Colorado, especially the San Luis Valley. If you're on a regulated public system, it has to keep arsenic below 10 ppb; the higher-risk situation is a private well in an affected area, which can run higher and isn't held to that limit.

Is Colorado water hard?

Often, yes. Aquifer studies show water in many parts of the state, including the San Luis Valley's Rio Grande aquifer, runs relatively hard thanks to dissolved calcium and magnesium. The good news is that hardness is an aesthetic and scaling nuisance (spots, scale, soap that won't lather), not a health limit, so it's about comfort and appliances rather than safety.

Do I need to test my well in Colorado?

If you're on a private well, yes. Private wells aren't federally regulated, which means no one else is checking them for you, and USGS data show parts of Colorado have elevated arsenic and nitrate. Testing for those two is the sensible starting point.

Water quality

Colorado water quality

If you're on a regulated public system in Colorado, the baseline is reassuring: most meet federal standards. The wrinkle here is geology rather than industry. According to USGS research and NPR reporting, parts of the state, especially the San Luis Valley, have naturally elevated arsenic (a contaminant that occurs in rock and seeps into groundwater) in their groundwater, and one USGS study predicted large areas could meet or exceed the 10 ppb arsenic standard. You'll also notice hard water, the dissolved minerals that scale up your fixtures, in areas drawing from mineral-rich aquifers. The people who carry the most risk are private well users, since wells aren't covered by those federal rules, so if that's you, this is worth a closer look.

Documented considerations

Arsenic

According to USGS modeling of Southwestern basin-fill aquifers, a large share of the area, including Colorado's San Luis Valley, was predicted to meet or exceed the 10 ppb arsenic standard; NPR reported rising valley arsenic linked to drought and aquifer overpumping.

What removes arsenic →

Hardness

According to studies of the Rio Grande aquifer serving the San Luis Valley, calcium and magnesium levels indicate relatively hard water, consistent with mineral-rich groundwater common across Colorado.

What removes hardness →

Nitrates

According to USGS basin-fill modeling, parts of Colorado including the San Luis Valley were among areas predicted to approach or exceed the 10 mg/L nitrate standard, a concern mainly for private wells in agricultural areas.

What removes nitrates →

Certified filters for Colorado's main concerns

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FAQ

Is there arsenic in Colorado drinking water?: In some places, yes, and it's natural rather than dumped there. USGS research and NPR reporting point to elevated arsenic in parts of Colorado, especially the San Luis Valley. If you're on a regulated public system, it has to keep arsenic below 10 ppb; the higher-risk situation is a private well in an affected area, which can run higher and isn't held to that limit.
Is Colorado water hard?: Often, yes. Aquifer studies show water in many parts of the state, including the San Luis Valley's Rio Grande aquifer, runs relatively hard thanks to dissolved calcium and magnesium. The good news is that hardness is an aesthetic and scaling nuisance (spots, scale, soap that won't lather), not a health limit, so it's about comfort and appliances rather than safety.
Do I need to test my well in Colorado?: If you're on a private well, yes. Private wells aren't federally regulated, which means no one else is checking them for you, and USGS data show parts of Colorado have elevated arsenic and nitrate. Testing for those two is the sensible starting point.

Sources

Not sure how to read your local report? See our guide on reading a water quality report.