We read 20 results from Castle Rock Town of’s 2025 water quality report. No results over a legal limit; 6 above a health goal or guideline.
Serves about 106,822 people · Water system ID CO0118010 · Read the district’s 2025 report (opens in a new tab)
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Results from the 2025 report
Each number is copied from the district’s report and links to the page it’s printed on. Where the report lists several plants, wells or purchased water, the highest is shown.
| Contaminant | Result | Health goal | Legal limit | What it means |
|---|---|---|---|---|
| Arsenicaverage · range ND to 3 · Entry points · 2025 report, page 10 | 0.64 ppb | 0.004 ppb | 10 ppb | Above the health goal160x the health goal |
| Bromateaverage · range ND to 5.6 · Entry points · 2025 report, page 9 | 2.46 ppb | 0.1 ppb | 10 ppb | Above the health goal25x the health goal |
| Gross alpha (radioactivity)average · range 0.89 to 6.6 · Entry points · 2025 report, page 11 | 2.6 pCi/L | 0 pCi/L | 15 pCi/L | Above the health goalThe health goal is zero |
| Lead90th percentile of 100 homes tested, 1 over the action level · Customer taps · 2025 report, page 11 | 2 ppb | 0.2 ppb | 15 ppb (action level) | Above the health goal10x the health goal |
| Radium (combined 226 + 228)average · range 0.5 to 4.1 · Entry points · 2025 report, page 11 | 2.52 pCi/L | 0 pCi/L | 5 pCi/L | Above the health goalThe health goal is zero |
| Uraniumaverage · range 3.7 to 11 · Entry points · 2025 report, page 11 | 7.09 ppb | 0.6 ppb | 30 ppb | Above the health goal12x the health goal |
| Bariumaverage · range 0.08 to 0.2 · Entry points · 2025 report, page 10 | 0.12 ppm | 2 ppm | 2 ppm | Below the health goal |
| Chlorideaverage · range 16 to 115 · Entry points · 2025 report, page 10 | 37 ppm | — | 250 ppm guideline | Within the guideline |
| Chromium (total)average · range 1 to 4 · Entry points · 2025 report, page 10 | 2.09 ppb | None set | 100 ppb | Below the legal limit |
| Copper90th percentile of 100 homes tested, 0 over the action level · Customer taps · 2025 report, page 11 | 0.16 ppm | 0.3 ppm | 1.3 ppm (action level) | Below the health goal |
| Disinfection byproducts (HAA5)average · range ND to 5.56 · Distribution system · 2025 report, page 9 | 2.09 ppb | None set | 60 ppb | Below the legal limit |
| Disinfection byproducts (TTHM)average · range 1.5 to 13.3 · Distribution system · 2025 report, page 9 | 6.18 ppb | None set | 80 ppb | Below the legal limit |
| Fluorideaverage · range 0.62 to 0.95 · Entry points · 2025 report, page 10 | 0.74 ppm | 1 ppm | 4 ppm | Below the health goal |
| Nitrate (as N)average · range ND to 1.5 · Entry points · 2025 report, page 10 | 0.33 ppm | 10 ppm | 10 ppm | Below the health goal |
| Seleniumaverage · range ND to 4 · Entry points · 2025 report, page 10 | 2.36 ppb | 30 ppb | 50 ppb | Below the health goal |
| Sulfateaverage · range 13 to 54 · Entry points · 2025 report, page 10 | 27 ppm | — | 250 ppm guideline | Within the guideline |
| Total dissolved solidsaverage · range 166 to 500 · Entry points · 2025 report, page 10 | 229 ppm | — | 500 ppm guideline | Within the guideline |
| Turbidity (cloudiness)highest measured · Entry points · 2025 report, page 9 | 0.04 NTU | None set | 1 NTU | Below the legal limit |
| Hardnessaverage · range 3.57 to 10.6 · Entry points · 2025 report, page 10 | 5.85 gpg (100 ppm) | — | — | Moderately hard |
| Sodiumaverage · range 11.4 to 69 · Entry points · 2025 report, page 10 | 33.8 ppm | None set | None | No health limit |
Utility results describe the whole system, measured where water enters the pipes, not your tap. Your home’s plumbing can add lead or copper.
EPA testing for PFAS and lithium
EPA’s own nationwide testing (UCMR 5) found these in Castle Rock Town of’s water between May 2023 and Feb 2024. These are EPA lab results, separate from the district’s report. Anything not listed was not detected.
- Lithium25 ppbFound in 11 of 12 samples · highest resultAbove EPA’s health reference level of 10 ppb (a guide, not a legal limit)
Source: EPA UCMR 5 occurrence data. The highest single result is shown; one high sample doesn’t mean every glass is that high.
What you can do
Nothing here is an emergency notice: if the district has a violation, it must tell customers directly. If you’d like to lower these at your tap, these are the treatments that remove them, and the catalog shows the models certified for each. Ranking is by certified removal; commissions never change the order.
Radium and uranium
Found: Gross alpha (radioactivity), Radium (combined 226 + 228), Uranium
What removes it: Reverse osmosis.
Lead
Found: Lead
What removes it: Certified carbon block or RO.
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