Water Quality Report · Updated October 07, 2026
THORNTON CITY OF
THORNTON CITY OF delivers tap water graded F (44/100) by TapWaterSafety.org. The utility serves approximately 226,465 residents in THORNTON, Colorado using surface water. The most significant water quality concerns are: PFAS contamination; Perfluorohexane sulfonate (PFHXS) significantly above health guideline; Haloacetic acids (HAA9) significantly above health guideline; Total trihalomethanes (TTHMs) significantly above health guideline. For questions, the utility can be reached at 303-255-7775.
Is THORNTON tap water safe to drink?
THORNTON CITY OF delivers tap water that earns a grade of F (44/100) from TapWaterSafety.org — a poor rating, with significant contamination concerns and/or recent violations.
The utility serves 226,465 residents in THORNTON, drawing from surface water.
Public testing data identifies 22 contaminants in this water above EWG's health-based guidelines, including: Perfluorohexane sulfonate (PFHXS), Haloacetic acids (HAA9), Total trihalomethanes (TTHMs), Bromodichloromethane, Dibromochloromethane, Dibromoacetic acid, Haloacetic acids (HAA5), Chromium (hexavalent), Perfluorooctanoic acid (PFOA), Dichloroacetic acid, Perfluorononanoic acid (PFNA), Chloroform, Perfluorodecanoic acid (PFDA), Bromoform, Bromate, Trichloroacetic acid, Radium, combined (-226 and -228), Perfluorooctane sulfonate (PFOS), Uranium, Nitrate, Nitrate and nitrite, Chlorate. For most residents, a properly certified home filter at the kitchen tap is the most cost-effective way to reduce exposure to whatever's in your water. See our filter recommendations below, matched specifically to this utility's contaminant profile.
EPA compliance record
Official U.S. EPA records for THORNTON CITY OF (system ID CO0101150) for the last 3 years. Checked 2026-10-07.
| Rule | Type | Since | Status |
|---|---|---|---|
| Interim and Long Term 1 Enhanced Surface Water Treatment Rule | Missed testing or reporting | 09/01/2023 | Resolved |
| Lead and Copper Rule | Missed testing or reporting | 07/01/2023 | Resolved |
Source: U.S. EPA Enforcement and Compliance History Online (ECHO), from the Safe Drinking Water Information System. See EPA's full report.
Quick actions for THORNTON residents
Top concerns in this water
Based on the most recent EPA and EWG data, these are the most significant water quality issues for THORNTON CITY OF.
PFAS contamination
Severe concernPerfluorononanoic acid (PFNA), Perfluorooctane sulfonate (PFOS) detected. PFAS are persistent chemicals linked to cancer and immune effects with no known safe exposure threshold.
Perfluorohexane sulfonate (PFHXS) significantly above health guideline
Moderate concernPerfluorohexane sulfonate (PFHXS) detected at 1.71 ppt, 1713x above the EWG health guideline of 0.001 ppt.
Haloacetic acids (HAA9) significantly above health guideline
Moderate concernHaloacetic acids (HAA9) detected at 31.3 ppb, 522x above the EWG health guideline of 0.06 ppb.
Total trihalomethanes (TTHMs) significantly above health guideline
Moderate concernTotal trihalomethanes (TTHMs) detected at 38.6 ppb, 257x above the EWG health guideline of 0.15 ppb.
Contact THORNTON CITY OF
Reach the utility directly for service issues, water quality concerns, or to request your Consumer Confidence Report.
General Contact
Treatment Plant
Recommended water filters for THORNTON
Filters matched to the specific contaminants in this water supply.
Filter certified for PFOA/PFOS (NSF/ANSI 53 or 58)
$180-$750Reverse osmosis and some carbon block filters reduce PFAS. Look for certification to NSF/ANSI 53 or 58 for PFOA/PFOS.
Carbon filter certified for VOCs (NSF/ANSI 53)
$180-$599Activated carbon is effective for disinfection byproducts. Look for NSF/ANSI 53 VOC reduction.
Disclosure: TapWaterSafety earns a commission from purchases made through these links. This does not influence our scoring methodology or filter selection.
Score breakdown
This utility's overall score of 44/100 breaks down across five weighted components. Read the full methodology →
Contaminants detected — international standards comparison
Every contaminant detected, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal (the strictest US benchmark). Why we show multiple standards →
| Contaminant | Detected | EWG US health-based |
EPA US legal |
EU DWD Europe |
WHO global |
CA PHG strictest US |
Tested sample year |
Status |
|---|---|---|---|---|---|---|---|---|
| Perfluorohexane sulfonate (PFHXS) PFAS |
1.71 ppt | 0.001 | 10.0 | — | — | — | — | 1713× over |
| Haloacetic acids (HAA9) Disinfection byproduct |
31.3 ppb | 0.06 | — | — | — | — | — | 522× over |
| Total trihalomethanes (TTHMs) Disinfection byproduct |
38.6 ppb | 0.15 | 80.0 | 100 | — | — | — | 257× over |
| Bromodichloromethane Disinfection byproduct |
11.8 ppb | 0.06 | — | — | — | — | — | 197× over |
| Dibromochloromethane Disinfection byproduct |
13.4 ppb | 0.1 | — | — | — | — | — | 134× over |
| Dibromoacetic acid Disinfection byproduct |
2.91 ppb | 0.03 | — | — | — | — | — | 97× over |
| Haloacetic acids (HAA5) Disinfection byproduct |
8.13 ppb | 0.1 | 60.0 | 60 | — | — | — | 81× over |
| Chromium (hexavalent) Heavy metal |
0.604 ppb | 0.02 | — | — | — | — | — | 30× over |
| Perfluorooctanoic acid (PFOA) PFAS |
2.55 ppt | 0.09 | 4.0 | 100 | 100 | 0.007 | — | 28× over |
| Dichloroacetic acid Disinfection byproduct |
4.02 ppb | 0.2 | — | — | — | — | — | 20× over |
| Perfluorononanoic acid (PFNA) PFAS |
0.114 ppt | 0.006 | 10.0 | — | — | — | — | 19× over |
| Chloroform Disinfection byproduct |
6.93 ppb | 0.4 | — | — | — | — | — | 17× over |
| Perfluorodecanoic acid (PFDA) PFAS |
0.089 ppt | 0.006 | — | — | — | — | — | 15× over |
| Bromoform Disinfection byproduct |
6.44 ppb | 0.5 | — | — | — | — | — | 13× over |
| Bromate Disinfection byproduct |
1.01 ppb | 0.1 | 10.0 | 10 | 10 | 0.1 | — | 10× over |
| Trichloroacetic acid Disinfection byproduct |
0.897 ppb | 0.1 | — | — | — | — | — | 9.0× over |
| Radium, combined (-226 and -228) Radiological |
0.31 pCi/L | 0.05 | 5.0 | — | — | — | — | 6.2× over |
| Perfluorooctane sulfonate (PFOS) PFAS |
1.46 ppt | 0.3 | 4.0 | 100 | 100 | 1 | — | 4.9× over |
| Uranium Radiological |
1.97 pCi/L | 0.43 | 20.0 | 30 | 30 | 0.43 | — | 4.6× over |
| Nitrate Inorganic |
0.355 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 2.5× over |
| Nitrate and nitrite Inorganic |
0.345 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 2.5× over |
| Chlorate Disinfection byproduct |
438.0 ppb | 210.0 | — | — | — | — | — | 2.1× over |
| Molybdenum Other |
3.71 ppb | 40.0 | — | — | — | — | — | Below guideline |
| Barium Heavy metal |
44.2 ppb | 700.0 | 2000.0 | — | 1300 | 2000 | — | Below guideline |
| Selenium Heavy metal |
0.267 ppb | 30.0 | 50.0 | 20 | 40 | 30 | — | Below guideline |
| Monobromoacetic acid Disinfection byproduct |
0.204 ppb | 25.0 | — | — | — | — | — | Below guideline |
| Perfluoropentanoic Acid (PFPeA) PFAS |
8.07 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Perfluorohexanoic Acid (PFHxA) PFAS |
7.85 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Perfluorobutanoic Acid (PFBA) PFAS |
7.3 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| 2,4-D Pesticide/Herbicide |
0.0748 ppb | 20.0 | 70.0 | — | — | — | — | Below guideline |
| Monochloroacetic acid Disinfection byproduct |
0.194 ppb | 53.0 | — | — | — | — | — | Below guideline |
| Perfluorobutane sulfonate (PFBS) PFAS |
5.19 ppt | 2000.0 | — | — | — | — | — | Below guideline |
| Manganese Heavy metal |
0.246 ppb | 100.0 | — | 50 | 80 | — | — | Below guideline |
| Perfluoroheptanoic acid (PFHPA) PFAS |
1.3 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Strontium Radiological |
0.287 ppb | 1500.0 | — | — | — | — | — | Below guideline |
| Fluoride Inorganic |
0.651 ppm | — | 4.0 | 1.5 | 1.5 | — | — | Below guideline |
| Lithium Other |
27.0 ppb | — | — | — | — | — | — | Below guideline |
All values in the unit of the detected level. Red cells indicate the detected level exceeds that standard. Some contaminants have limits in some jurisdictions but not others (shown as —). The "Tested" column shows the year each contaminant sample was collected.
Sources: US EPA, EU Drinking Water Directive 2020/2184, WHO Guidelines (4th ed.), California OEHHA PHGs, EWG Tap Water Database.
THORNTON CITY OF service area
This water system serves 1 community in Adams County, Colorado. Click any city for its dedicated tap water quality page.
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