Douglas County Water Quality: 3 Cities Ranked by the Records
Douglas County, Colorado: 3 city reports built from EPA and utility records. A county has many suppliers; each city shows the system that serves it.
Highest result for each contaminant
One row per contaminant: the highest result any system in the county reported, against its limit. Open a row for the systems behind it.
LithiumDetected in 2 systems10 µg/L EPA health reference level (screening, not a legal limit) · US EPAHighest27.6 µg/L
- PARKER WSD27.6 µg/LSample date: 2024-04-01 to 2025-07-01
- CASTLE ROCK TOWN OF25 µg/LSample date: 2023-05-25 to 2024-02-21
Perfluorooctanoic acid (PFOA)Detected in 1 system of 2 tested4.0 ng/L federal MCL (2024) · US EPAHighest4.8 ng/L
- PARKER WSD4.8 ng/LSample date: 2024-04-01 to 2025-07-01
- CASTLE ROCK TOWN OFNot detected · below 4.0 ng/L lab reporting limitSample date: 2023-05-25 to 2024-02-21
Lead (90th percentile)Detected in 3 systems15 µg/L federal action level · US EPAHighest9 µg/L
- SOUTHGATE WSD9 µg/LMonitoring period: 2002–2002
- PARKER WSD2.6 µg/LMonitoring period: 2026–2026 (still open)
- CASTLE ROCK TOWN OF2 µg/LMonitoring period: 2026–2026 (still open)
Perfluorobutanesulfonic acid (PFBS)Detected in 1 system of 2 tested2,000 ng/L EPA health advisory (screening, not a legal limit) · US EPAHighest4.6 ng/L
- PARKER WSD4.6 ng/LSample date: 2024-04-01 to 2025-07-01
- CASTLE ROCK TOWN OFNot detected · below 3.0 ng/L lab reporting limitSample date: 2023-05-25 to 2024-02-21
Perfluorohexanoic acid (PFHxA)Detected in 1 system of 2 tested400,000 ng/L Michigan EGLE state MCL (strictest US state) · Michigan EGLEHighest11.9 ng/L
- PARKER WSD11.9 ng/LSample date: 2024-04-01 to 2025-07-01
- CASTLE ROCK TOWN OFNot detected · below 3.0 ng/L lab reporting limitSample date: 2023-05-25 to 2024-02-21
Perfluorobutanoic acid (PFBA)Detected in 2 systemsNo federal or state limit; shown for transparencyHighest8.6 ng/L
- PARKER WSD8.6 ng/LSample date: 2024-04-01 to 2025-07-01
- CASTLE ROCK TOWN OF5.1 ng/LSample date: 2023-05-25 to 2024-02-21
Perfluoropentanoic acid (PFPeA)Detected in 2 systemsNo federal or state limit; shown for transparencyHighest14 ng/L
- PARKER WSD14 ng/LSample date: 2024-04-01 to 2025-07-01
- CASTLE ROCK TOWN OF4.7 ng/LSample date: 2023-05-25 to 2024-02-21
24 PFAS tested, none detected in any systemShow
Tested in these 2 systems: CASTLE ROCK TOWN OF, PARKER WSD
- 11-Chloroeicosafluoro-3-oxaundecane-1-sulfonic acid (11Cl-PF3OUdS)
- 1H, 1H, 2H, 2H-perfluorodecane sulfonic acid (8:2 FTS)
- 1H, 1H, 2H, 2H-perfluorohexane sulfonic acid (4:2 FTS)
- 1H, 1H, 2H, 2H-perfluorooctane sulfonic acid (6:2 FTS)
- 4,8-Dioxa-3H-perfluorononanoic acid (ADONA)
- 9-Chlorohexadecafluoro-3-oxanone-1-sulfonic acid (9Cl-PF3ONS)
- Hexafluoropropylene oxide dimer acid (HFPO-DA) (GenX chemicals)
- N-ethyl perfluorooctanesulfonamidoacetic acid (NEtFOSAA)
- N-methyl perfluorooctanesulfonamidoacetic acid (NMeFOSAA)
- Nonafluoro-3,6-dioxaheptanoic acid (NFDHA)
- Perfluoro (2-ethoxyethane) sulfonic acid (PFEESA)
- Perfluoro-3-methoxypropanoic acid (PFMPA)
- Perfluoro-4-methoxybutanoic acid (PFMBA)
- Perfluorodecanoic acid (PFDA)
- Perfluorododecanoic acid (PFDoA)
- Perfluoroheptanesulfonic acid (PFHpS)
- Perfluoroheptanoic acid (PFHpA)
- Perfluorohexanesulfonic acid (PFHxS)
- Perfluorononanoic acid (PFNA)
- Perfluorooctanesulfonic acid (PFOS)
- Perfluoropentanesulfonic acid (PFPeS)
- Perfluorotetradecanoic acid (PFTA)
- Perfluorotridecanoic acid (PFTrDA)
- Perfluoroundecanoic acid (PFUnA)
Cities ranked by the records
Ranked by the Purity Score of each city's main water system, highest first. Scores belong to water systems; there is no county score. The score is computed only from contaminants measured in the published EPA record, so this ranks the record, not which city's water is safest. How the score works.
0of 3 cities above the 15 µg/L action level
Based on each system's 90th-percentile result. Lead from household plumbing isn't in this record.
Lead in ColoradoLargest water systems
- Castle RockCASTLE ROCK TOWN OF · CO0118010110,298 served
- ParkerPARKER WSD · CO011804075,949 served
- Lone TreeSOUTHGATE WSD · CO010372155,000 served
Frequently asked
How does Douglas County tap water compare across cities?
PurityMap ranks 3 cities in Douglas County by the Purity Score of each city's main water system, computed only from contaminants measured in the published EPA record. Scores belong to water systems, not to cities. The highest published score is Castle Rock's main water system: CASTLE ROCK TOWN OF · PWSID CO0118010 · Purity Score 98 (Excellent) · Confidence: moderate · Assessed at the water-system level. The ranking compares the records, not which city's water is safest, and your own tap can differ with household plumbing.
How many Douglas County cities had a PFAS sample above a 2024 EPA limit?
1 of 3 Douglas County city reports had a PFAS sample above a 2024 EPA limit in EPA's UCMR 5 testing, including Parker (PFOA 4.8 ng/L). That limit is judged on a yearly average, and water systems have until 2029 to meet it, so a single sample is not a violation. PFAS were detected at any level in 2.
Is there lead in Douglas County tap water?
Utilities report lead as a 90th-percentile result from home taps. 2 of 3 Douglas County cities reported a value above zero, and none was above the 15 µg/L federal action level. Lead usually comes from a building's own pipes and fixtures, so only a test at your tap tells you what you drink.
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