Thornton City Of
Thornton, Colorado · PWSID: CO0101150
Thornton Water Quality Summary
Thornton City Of supplies drinking water to about 226,465 people in Thornton, Colorado, and draws from surface water (rivers, lakes, or reservoirs), which requires fuller treatment for runoff, sediment, and microbial risk. On the IsWaterSafe scale it earns a fair Water Safety Score of 70 out of 100 (Grade C), a composite of its EPA SDWIS violation and contaminant record.
This system has no health-based violations on record, but EPA logs 13 monitoring violations — failures to test or report water quality on schedule rather than confirmed contamination. 22 enforcement actions are recorded against the system.
Across the 5 substances sampled, none exceeded its EPA limit. Chlorine sits highest relative to its ceiling, detected at 2 ppm against an MCL of 4 ppm (sampled May 2021) — within the legal limit.
The most recent documented episode is a health-based violation involving Gross Beta, beginning April 2022 and marked resolved August 2022.
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Detected Contaminants
| Contaminant | Detected Level | MCL (Limit) | Status | Sample Date |
|---|---|---|---|---|
| Chlorine | 2 ppm | 4 ppm | Within Limit | May 1, 2021 |
| Gross Beta | 25 pCi/L | 50 pCi/L | Within Limit | Apr 1, 2022 |
| Uranium | 15 ppb | 30 ppb | Within Limit | Apr 1, 2022 |
| Gross Alpha | 7.5 pCi/L | 15 pCi/L | Within Limit | Apr 1, 2022 |
| Combined Filter Effluent | 0.5 NTU | 1 NTU | Within Limit | Jul 1, 2023 |
Violation History
Frequently Asked Questions
Thornton City Of has a Water Safety Score of C (70/100). The system serves 226,465 people and has 0 health violations on record. Check the contaminant table above for specific detected substances.
Thornton City Of has 0 contaminant exceedances above EPA health guidelines. See the full contaminant detection table above for all tested substances and their levels relative to legal limits and health guidelines.
The Water Safety Score (0-100, grades A through F) is based on contaminant levels relative to legal limits, health guideline exceedances, violation history, and enforcement actions. Higher scores indicate fewer concerns.
If your water system has violations, request the Consumer Confidence Report from your utility, consider getting an independent water test from a certified lab, and look into certified water filters for specific contaminants of concern. For lead, run cold water for 30 seconds before drinking.
Water quality data sourced from EPA's Safe Drinking Water Information System (SDWIS). Safety scores are calculated based on contaminant levels, violations, and enforcement history. This is not a substitute for your utility's official Consumer Confidence Report.
Source: EPA Ground Water and Drinking Water, 2026.