Is Thornton, CO Tap Water Safe to Drink?
Graded F — but NDMA and Chlorate were detected above EPA limits. Here's what's in the water and how to remove it. What to do next ↓
38/100
waterverge.com Thornton, CO — Water Quality Report
Thornton's drinking water received a grade of F (38 out of 100), indicating failing water quality. The city's 9 water systems serve approximately 233,094 residents using surface water.
Lead levels were measured at 0.0 ppb (90th percentile), well within EPA limits. UCMR 5 testing detected 9 PFAS compounds, with levels exceeding EPA maximum contaminant levels in the water supply.
The system has 139 violations on record, including 3 health-based violations. 29 remain unresolved.
What to know about Thornton's water
Thornton ranks #238 out of 246 cities in Colorado for water quality, placing it among the lowest-rated in the state.
The city draws from surface water sources, which are more susceptible to seasonal runoff and agricultural contamination, requiring extensive multi-barrier treatment including coagulation, filtration, and disinfection.
Of particular concern: PFAS "forever chemical" levels exceed the 2024 EPA maximum contaminant levels. These synthetic compounds don't break down naturally and require specialized filtration such as reverse osmosis or granular activated carbon.
Hexavalent chromium (chromium-6) was detected at 1.00 µg/L in UCMR 3 testing. While below California's 10 µg/L limit and with no federal MCL set, residents sensitive to this contaminant may consider reverse osmosis filtration.
The system has seen 133 violations in the past five years, suggesting a pattern of compliance challenges that residents should monitor closely.
Water quality score
See methodology →Is Thornton, CO water safe to drink?
Thornton's drinking water has significant quality concerns based on EPA testing data. With a grade of F (38/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 9 water systems serve approximately 233,094 residents using surface water (rivers, lakes, or reservoirs).
Recent water quality updates for Thornton
A timeline of significant water quality events, violations, and data updates.
PFAS levels exceed EPA maximum contaminant levels. Reverse osmosis or activated carbon filtration recommended.
Latest EPA compliance and testing data incorporated into Thornton's water quality assessment. Grade: F (38/100).
Contaminants: Lead and Copper Rule.
Contaminants: Public Notice.
Contaminants: Lead and Copper Rule.
Federal disaster declaration (FEMA DR-4229). Flood event — may have impacted local water infrastructure.
Key contaminant findings
Based on the most recent EPA sampling data for Thornton's water supply.
Well within EPA limits.
PFAS "forever chemicals" exceed EPA maximum contaminant levels. Reverse osmosis or granular activated carbon filtration strongly recommended.
PFAS "forever chemicals" detected
UCMR 5 testing found 9 PFAS compounds in Thornton's water supply. PFAS are synthetic chemicals that persist indefinitely in the environment and the human body.
Violation history
Thornton's water system has 139 total violations on record, including 3 health-based violations. 29 remain unresolved. 133 violations were issued in the last 5 years.
Flood & environmental risk
Adams County has experienced 6 federally declared disasters since 1969. Flooding and severe storms can overwhelm water treatment plants, cause sewage overflows, and introduce agricultural runoff, bacteria, and sediment into drinking water supplies. Local water sources include Dry Gulch, Lakewood Gulch, Cherry Creek, South Platte R, Sand Crk.
Where does Thornton's water come from?
Thornton's drinking water comes from surface water (rivers, lakes, or reservoirs), supplied by 9 water systems serving approximately 233,094 people. Surface water sources are more susceptible to contamination from runoff, industrial discharge, and algal blooms, requiring extensive treatment. Nearby water bodies include Dry Gulch (river), Lakewood Gulch (river), Cherry Creek (river), South Platte R (river), Sand Crk (river).
What Thornton residents can do
Recommended: Reverse osmosis system. This addresses the specific contaminants found in Thornton's water.
Your water utility is required to publish an annual Consumer Confidence Report (CCR) with detailed testing results. Ask for the latest copy or check your utility's website.
Thornton's area has a history of flooding. After severe weather, watch for boil water advisories from your local utility.
Data: EPA SDWIS, UCMR 5 (PFAS), FEMA, NOAA. Last updated May 2026.
Top contaminants to know
View all ↓Forever chemicals overview
National PFAS report →Violation summary
Violations & advisories
Top industrial polluters within 10 miles of Thornton
Industrial polluters nearby
Reported releases to surface water by facilities near Thornton, ranked by pounds discharged annually.
Total reported releases to surface water: 693 lbs
| Facility | Top chemical | To surface water (lbs/yr) | Distance |
|---|---|---|---|
SUNCOR ENERGY COMMERCE CITY REFINERY COMMERCE CITY, CO80022 | Ammonia | 630 | 8.2 mi |
NESTLE PURINA PETCARE CO DENVER, CO80216 | Manganese And Manganese Compounds | 61 | 9.8 mi |
BAND IT IDEX INC DENVER, CO80216 | Nickel | 2 | 9.5 mi |
OWENS CORNING ROOFING & ASPHALT LLC DENVER, CO80216 | Polycyclic aromatic compounds | 0 | 9.3 mi |
OWENS CORNING ROOFING & ASPHALT LLC DENVER, CO80216 | Polycyclic aromatic compounds | 0 | 9.3 mi |
Source: EPA Toxic Release Inventory (TRI) 2023
Superfund sites within 10 miles of Thornton
Superfund sites nearby
Federally tracked hazardous-waste sites on the EPA National Priorities List. Proximity does not necessarily indicate tap-water contamination — the connection depends on hydrology and treatment.
- CHEMICAL SALES CO6.9 mi
- ROCKY MOUNTAIN ARSENAL USARMY8.0 mi
- BRODERICK WOOD PRODUCTS8.6 mi
- VASQUEZ BOULEVARD AND I 708.9 mi
Source: EPA Superfund National Priorities List
Drought conditions
D3 — extreme droughtAdams County is currently in D3 (extreme drought) per the U.S. Drought Monitor (week of May 5, 2026). Drought can elevate disinfection-byproduct (TTHM/HAA5) levels and taste/odor issues as utilities draw from lower reservoirs.
Source: U.S. Drought Monitor, updated weekly by NDMC, USDA, and NOAA.
Flood & disaster history
Adams County has experienced 6 federally declared disasters since 1969. Flooding and severe weather can compromise water treatment infrastructure and introduce contaminants into drinking water supplies.
Recommended water filters
Based on contaminants detected in Thornton's water supply, we recommend the following filter types.
Full contaminants report
| Contaminant | Detected Level | EPA Limit | Unit | Category | Status |
|---|---|---|---|---|---|
| Lead (90th percentile) LeadHeavy Metal A toxic heavy metal that can leach into drinking water from older pipes, solder, and fixtures. No amount of lead in water is considered safe. Health EffectsBrain and nervous system damage in children, kidney damage, high blood pressure, and reproductive problems in adults. EPA Limit15 ppb action level Common SourcesCorrosion of lead pipes, lead solder, brass faucets, and household plumbing. | 0.0 | 15 | ppb | Inorganic | Safe |
| 11Cl-PF3OUdS | ND | HI | µg/L | PFAS | Not Detected |
| 4:2 FTS | ND | HI | µg/L | PFAS | Not Detected |
| 6:2 FTS 6:2 FTSPFAS A fluorotelomer sulfonate commonly found at sites contaminated with aqueous film-forming foam (AFFF) used in firefighting. Health EffectsPotential liver toxicity and endocrine disruption. Less studied but identified as a contaminant of concern. EPA LimitNo individual MCL (not yet regulated) Common SourcesFirefighting foam (AFFF), airports, military bases, and industrial facilities. | ND | HI | µg/L | PFAS | Not Detected |
| 8:2 FTS | ND | HI | µg/L | PFAS | Not Detected |
| 9Cl-PF3ONS | ND | HI | µg/L | PFAS | Not Detected |
| ADONA | ND | HI | µg/L | PFAS | Not Detected |
| HFPO-DA HFPO-DA (GenX)PFAS A replacement for PFOA in manufacturing, marketed as safer but still a persistent "forever chemical." Also known as GenX. Health EffectsLiver and kidney effects, reproductive toxicity, immune system effects, and potential cancer risk. EPA Limit10 ppt MCL Common SourcesFluoropolymer manufacturing (used as PFOA replacement), industrial wastewater discharge. | ND | 0.01 | µg/L | PFAS | Not Detected |
| lithium LithiumInorganic A naturally occurring alkali metal found in groundwater. Monitored under UCMR 5 to assess occurrence in drinking water. Health EffectsKidney effects at high doses. Low-level exposure effects under study; some research suggests neurological effects. EPA LimitNo MCL (monitoring only under UCMR 5) Common SourcesNatural mineral deposits, geothermal water, and industrial discharge. | 34.000 | HI | µg/L | PFAS | Detected |
| NEtFOSAA | ND | HI | µg/L | PFAS | Not Detected |
| NFDHA | ND | HI | µg/L | PFAS | Not Detected |
| NMeFOSAA | ND | HI | µg/L | PFAS | Not Detected |
| PFBA PFBAPFAS One of the shortest-chain PFAS compounds. Very mobile in water and difficult to remove with standard filtration. Health EffectsThyroid effects, potential developmental toxicity. Shorter half-life in body than long-chain PFAS. EPA LimitNo individual MCL (not yet regulated) Common SourcesDegradation of longer-chain PFAS, industrial discharge, and firefighting foam. | 0.010 | HI | µg/L | PFAS | Detected |
| PFBS PFBSPFAS A short-chain PFAS used as a replacement for PFOS. While it clears the body faster than long-chain PFAS, it still persists in the environment. Health EffectsThyroid effects, reproductive and developmental toxicity, kidney effects. EPA LimitPart of Hazard Index (1.0) Common SourcesIndustrial discharge, firefighting foam, and as a replacement chemical in manufacturing. | 0.008 | HI | µg/L | PFAS | Detected |
| PFDA | ND | HI | µg/L | PFAS | Not Detected |
| PFDoA | ND | HI | µg/L | PFAS | Not Detected |
| PFEESA | ND | HI | µg/L | PFAS | Not Detected |
| PFHpA PFHpAPFAS A medium-chain PFAS compound found in various environmental samples. Less studied than PFOA/PFOS but still considered a contaminant of concern. Health EffectsLiver effects, potential developmental toxicity, and endocrine disruption. EPA LimitPart of Hazard Index (1.0) Common SourcesDegradation of longer-chain PFAS, industrial discharge, and contaminated water sources. | 0.004 | HI | µg/L | PFAS | Detected |
| PFHpS | ND | HI | µg/L | PFAS | Not Detected |
| PFHxA PFHxAPFAS A short-chain PFAS replacement chemical widely used after manufacturers phased out longer-chain PFAS. Very commonly detected in water. Health EffectsLiver and kidney effects, potential thyroid disruption. Considered less toxic than long-chain PFAS but still persistent. EPA LimitNo individual MCL (not yet regulated) Common SourcesIndustrial processes, firefighting foam (AFFF), food packaging, and textile treatment. | 0.013 | HI | µg/L | PFAS | Detected |
| PFHxS PFHxSPFAS A medium-chain PFAS found in firefighting foam and consumer products. It has a long half-life in the human body, similar to long-chain PFAS. Health EffectsImmune system effects, thyroid disruption, and potential reproductive and developmental harm. EPA LimitPart of Hazard Index (1.0) Common SourcesFirefighting foam (AFFF), waterproof textiles, food packaging, and industrial discharge. | 0.006 | HI | µg/L | PFAS | Detected |
| PFMBA | ND | HI | µg/L | PFAS | Not Detected |
| PFMPA | ND | HI | µg/L | PFAS | Not Detected |
| PFNA PFNAPFAS A long-chain PFAS compound used in manufacturing fluoropolymers. It bioaccumulates in the body and is very persistent in the environment. Health EffectsDevelopmental effects, liver toxicity, immune suppression, and potential cancer risk. EPA LimitPart of Hazard Index (1.0) Common SourcesFluoropolymer manufacturing, industrial emissions, and contaminated water sources. | ND | HI | µg/L | PFAS | Not Detected |
| PFOA PFOAPFAS A long-chain PFAS ("forever chemical") once widely used in nonstick coatings and firefighting foam. It persists in the body and environment for years. Health EffectsLinked to kidney and testicular cancer, thyroid disease, elevated cholesterol, and reproductive issues. EPA Limit4.0 ppt MCL Common SourcesIndustrial discharge, firefighting foam (AFFF), nonstick cookware manufacturing, and contaminated groundwater. | 0.007 | 0.004 | µg/L | PFAS | Over MCL |
| PFOS PFOSPFAS A long-chain PFAS compound historically used in stain-resistant coatings and firefighting foam. One of the most studied and persistent PFAS chemicals. Health EffectsLiver damage, immune system suppression, thyroid disruption, increased cholesterol, and potential cancer risk. EPA Limit4.0 ppt MCL Common SourcesFirefighting foam (AFFF), industrial sites, stain-resistant fabric treatments, and contaminated groundwater. | 0.005 | 0.004 | µg/L | PFAS | Over MCL |
| PFPeA PFPeAPFAS A short-chain PFAS compound commonly detected in drinking water. One of the most frequently found PFAS in UCMR 5 monitoring. Health EffectsLess studied than PFOA/PFOS. Potential liver and thyroid effects. Research is ongoing. EPA LimitNo individual MCL (not yet regulated) Common SourcesIndustrial discharge, firefighting foam degradation, and consumer products. | 0.012 | HI | µg/L | PFAS | Detected |
| PFPeS | ND | HI | µg/L | PFAS | Not Detected |
| PFTA | ND | HI | µg/L | PFAS | Not Detected |
| PFTrDA | ND | HI | µg/L | PFAS | Not Detected |
| PFUnA | ND | HI | µg/L | PFAS | Not Detected |
Lead level trend (90th percentile)
See how Thornton compares by contaminant
Explore where Thornton ranks among all Colorado cities for specific contaminants.
Water source & infrastructure
Where Thornton's water comes from
Thornton's drinking water comes primarily from surface water sources such as rivers, lakes, or reservoirs.
Surface water systems require multi-stage treatment including coagulation, sedimentation, filtration, and disinfection to meet EPA Safe Drinking Water Act standards.
These sources can be impacted by seasonal changes, stormwater runoff, upstream agriculture, and industrial discharge.
The system is operated by local government ownership and serves approximately 233,094 people through 9 water systems.
Water bodies near Thornton
Thornton is located near 5 notable water bodies. As a surface water system, these water bodies may directly influence the city's drinking water supply.
Water systems serving Thornton
| System Name | PWSID | Population | Source |
|---|---|---|---|
| THORNTON CITY OF | CO0101150 | 226,465 | SW |
| WOODLAND HILLS MHC | CO0101833 | 1,740 | SWP |
| REDWOOD ESTATES | CO0101667 | 1,500 | SWP |
| THE GROVE AT ALTA RIDGE | CO0101320 | 1,300 | SWP |
| FRIENDLY VILLAGE OF THE ROCKIES | CO0101283 | 1,046 | SWP |
| AVILLA EASTLAKE | CO0101126 | 410 | SWP |
| CHAPARRAL VILLAGE MHP | CO0101078 | 303 | SWP |
| THORNTON ESTATES | CO0101741 | 300 | SWP |
| G AND M MOBILE HOME PARK | CO0153300 | 30 | GW |
How Thornton compares
Full Colorado rankings →Thornton's score of 38/100 is below the average of 45/100 among major Colorado cities. It outscores 2 of 10 nearby cities. 8 of 10 nearby cities score higher.
Nearby cities
View Colorado rankings →About Thornton, CO
Wikipedia →Thornton is a home rule city located in Adams and Weld counties, Colorado, United States. The city population was 141,867, all in Adams County, at the 2020 United States census, an increase of 19.44% since the 2010 United States census. Thornton is the sixth-most-populous city in Colorado and the 191st-most-populous city in the United States. Thornton is 10 miles (16 km) north of the Colorado State Capitol in Denver and is a part of the Denver-Aurora-Greeley, CO Combined Statistical Area and the Front Range Urban Corridor.
Learn more about your water
Guides and resources related to Thornton's water quality findings.
Explore water quality across Adams
Frequently asked questions
Is Thornton, CO tap water safe to drink?
Thornton's water quality earned a grade of F (38/100). Significant issues have been found. A water filter is strongly recommended. The city ranks #238 out of 246 cities tested in Colorado.
What contaminants are in Thornton's water?
Lead was measured at 0.0 ppb (90th percentile). 9 PFAS compounds were detected. 139 violations are on record.
How is Thornton's water quality grade calculated?
The grade is based on four factors: violation history (40%), lead and copper levels (25%), PFAS contamination (25%), and regulatory compliance (10%). The score is also adjusted based on how complete the available data is. See our methodology page for full details.
Do I need a water filter in Thornton?
PFAS compounds exceed EPA limits — a reverse osmosis or activated carbon filter is recommended.
Where does Thornton's water come from?
Thornton's water is sourced from Surface water. The city has 9 water systems serving approximately 233,094 residents.
What health violations has Thornton's water system had?
Thornton has 3 health-based violations on record. The most recent violation was recorded in January 2026. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 29 violations remain unresolved.
Why does Thornton have so many PFAS compounds in its water?
9 different PFAS "forever chemical" compounds were detected in Thornton's water supply during UCMR 5 testing. PFAS contamination often originates from proximity to military installations (AFFF firefighting foam), airports, industrial manufacturing sites, or wastewater treatment facilities. Some levels exceed the 2024 EPA maximum contaminant levels — a reverse osmosis or NSF-certified activated carbon filter is strongly recommended.
How does Thornton's water compare to other cities?
Thornton ranks #238 out of 246 cities in Colorado (better than 3% of state cities) and #15365 out of 15744 cities nationally (2th percentile). The grade of F reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.