Well Water in Colorado
Contaminant risks, testing requirements, and treatment recommendations for private well owners in Colorado.
Colorado Geology and Groundwater
Colorado sits on Rocky Mountain fractured bedrock and High Plains aquifer. This geology directly determines what contaminants are likely in private well water. Based on this geology, Colorado well owners face elevated risk for radon from granitic geology, uranium from bedrock geology. Moderate risk exists for arsenic, nitrate, PFAS.
Contaminant Risk Profile
| Contaminant | Risk Level | Why |
|---|---|---|
| Arsenic | Moderate risk | Some geological zones have elevated levels. Test recommended. |
| Nitrate | Moderate risk | Some areas near farmland or septic systems may have elevated levels. |
| Radon | Elevated risk | Granitic and metamorphic bedrock produces radon gas. Inhaled from water during showering. |
| PFAS | Moderate risk | Some known contamination sites exist. Check EWG's PFAS map for your area. |
| Iron/Manganese | Moderate risk | Found in some wells depending on local geology. |
| Uranium | Elevated risk | Natural occurrence in granitic/metamorphic bedrock. EPA MCL: 30 ppb. |
| Fluoride | Moderate risk | Some wells may have naturally elevated levels. |
How Colorado Compares: Municipal Water Data
CheckMyTap tracks water quality for 23 cities in Colorado. While these numbers reflect municipal water (not private wells), they indicate the baseline mineral content of Colorado's water sources. Private wells often draw from the same aquifers but with less treatment.
| Metric | Colorado Average | National Average |
|---|---|---|
| Hardness | 99 PPM (moderately hard) | 170 PPM |
| Hardness range | 40 - 210 PPM | 25 - 400+ PPM |
| Lead (avg municipal) | 3.2 ppb | 3.2 ppb |
| Nitrate (avg municipal) | 0.3 mg/L | 1.1 mg/L |
| Cities with PFAS detected | 6 of 23 | ~45% nationally |
| Cities exceeding PFAS MCL (4 ppt) | 6 |
Hardest water in Colorado: Parker (210 PPM), Castle Rock (200 PPM), Brighton (160 PPM), Greeley (152 PPM), Lafayette (150 PPM).
Softest water: Boulder North (40 PPM), Durango (45 PPM), Westminster (66 PPM).
Testing Requirements in Colorado
Colorado does not have a statewide mandatory testing requirement for existing private wells. Regardless of state requirements, the EPA recommends testing annually for:
- Every year: Total coliform bacteria, E. coli, nitrate, pH, and total dissolved solids
- At least once: Arsenic, lead, copper, fluoride, and any contaminant identified as a local risk
- Recommended for Colorado: Radon in water (granitic bedrock states have higher risk)
- Recommended for Colorado: PFAS panel, especially if near military bases or industrial sites
- Recommended for Colorado: Uranium, especially in areas with granitic or metamorphic bedrock
- After events: Retest after flooding, well repairs, nearby construction, or any change in taste/color/odor
Recommended Treatment for Colorado Wells
Based on Colorado's geology and common contaminant risks, these treatment systems address the most likely issues:
Removes arsenic, uranium, and most dissolved contaminants from drinking water
Learn moreMost effective radon-in-water removal (95-99%). GAC is an alternative for lower levels
Kills bacteria and viruses without chemicals. Recommended for all well water systems
Frequently Asked Questions
Is well water in Colorado safe to drink?
Well water quality in Colorado varies significantly by location and geology. Colorado sits on Rocky Mountain fractured bedrock and High Plains aquifer. Key concerns include radon from granitic geology, uranium from bedrock geology. The only way to know your specific water quality is to test it. Use our free interpreter to understand your results.
How often should I test my well water in Colorado?
The EPA recommends testing annually for bacteria (total coliform, E. coli), nitrate, total dissolved solids, and pH. Given Colorado's arsenic risk, test for arsenic at least once and after any changes to your well. Radon testing is also recommended in Colorado. Test more frequently if you notice changes in taste, color, or odor, or after flooding, nearby construction, or well repairs.
Does Colorado require well water testing?
Colorado does not have a statewide mandatory testing requirement for existing private wells. However, the EPA strongly recommends annual testing regardless of state requirements. Your county health department may have additional local requirements.
What is the average water hardness in Colorado?
Municipal water in Colorado averages 99 PPM across 23 cities tracked by CheckMyTap, ranging from 40 to 210 PPM. Private well water typically runs 20-50% harder than city water because groundwater has more contact time with mineral formations. Many Colorado well owners have manageable hardness levels, though local variation is significant. Check your city's data.