Yes, at low levels. 2 PFAS were detected, all below EPA's 2024 limits.
Also detected, no federal limit: PFBA, PFPeA.
Town of Castle Rock is a public water system drawing on surface water, based in Castle Rock, Colorado, serving about 110,298 people. Under EPA's Fifth Unregulated Contaminant Monitoring Rule it was tested for 29 PFAS and lithium 12 times across 5 sampling points between May 2023 and Aug 2024.
| PFAS | Detected | Highest | Worst point avg | EPA limit |
|---|---|---|---|---|
| PFBA Perfluorobutanoic acid |
1 of 12 | 5.1 ppt | 1.3 ppt | none |
| PFPeA Perfluoropentanoic acid |
2 of 12 | 4.7 ppt | 1.9 ppt | none |
Not detected: PFEESA, 8:2 FTS, PFMBA, PFMPA, NFDHA, PFPeS, PFHpS, PFBS, 4:2 FTS, PFTA, PFTrDA, NEtFOSAA, NMeFOSAA, PFDoA, PFHpA, PFHxS, PFNA, PFOS, 9Cl-PF3ONS, PFDA, 6:2 FTS, PFHxA, PFUnA, 11Cl-PF3OUdS, ADONA, HFPO-DA, PFOA.
Lithium, tested in the same program: highest 25 ppb, detected in 11 of 12 samples. EPA's health-based screening level is 10 ppb.
In April 2024 EPA set enforceable limits of 4 ppt for PFOA and PFOS, 10 ppt each for PFHxS, PFNA and GenX, and a hazard index of 1 for mixtures. Utilities were given until 2029 to comply. In May 2026 EPA proposed keeping only the PFOA and PFOS limits and moving that deadline to 2031. Until that proposal is final, the 2024 limits stand.
Compliance is judged on a running annual average at each entry point, so we show the average at this system's worst sampling point next to its single highest result. UCMR 5 results do not by themselves put a utility in or out of compliance.
Levels here are under EPA's limits, so no treatment is required. If you want them lower anyway, a certified reverse osmosis system under the sink handles drinking water, and a whole-house carbon filter also takes out the chlorine or chloramine your utility adds.
All 165 tested systems in Colorado
80104 80108 80109
As reported by the utility to EPA. Neighbouring ZIPs are often split between systems; your water bill names yours.
Well & Tap. "PFAS in Town of Castle Rock water: EPA UCMR 5 results." Data: U.S. EPA Fifth Unregulated Contaminant Monitoring Rule, final release August 2026, PWSID CO0118010. https://wellandtap.com/pfas/colorado/town-of-castle-rock/
Source: U.S. EPA, UCMR 5 occurrence data, final release August 2026 (PWSID CO0118010). Population: EPA SDWIS. Averages count results below the reporting level as zero, the same convention EPA uses for running annual averages. Full method.
