Tap Water Quality Report
Tap water quality in CASTLE ROCK, Colorado
Tap water in CASTLE ROCK, Colorado receives a grade of C (75/100) from TapWaterSafety.org. It's served by CASTLE ROCK TOWN OF. The most significant water quality concerns are: Arsenic significantly above health guideline; Haloacetic acids (HAA9) significantly above health guideline; Radium, combined (-226 and -228) significantly above health guideline. Data sources: EPA SDWIS, EPA ECHO, EWG Tap Water Database.
What's in CASTLE ROCK's tap water
Top water quality concerns identified by the EPA and Environmental Working Group across the utility serving CASTLE ROCK.
Arsenic significantly above health guideline
Moderate concernArsenic detected at 0.348 ppb, 87x above the EWG health guideline of 0.004 ppb.
Haloacetic acids (HAA9) significantly above health guideline
Moderate concernHaloacetic acids (HAA9) detected at 3.02 ppb, 50x above the EWG health guideline of 0.06 ppb.
Radium, combined (-226 and -228) significantly above health guideline
Moderate concernRadium, combined (-226 and -228) detected at 2.33 pCi/L, 47x above the EWG health guideline of 0.05 pCi/L.
EPA compliance record
Official U.S. EPA records for CASTLE ROCK TOWN OF (system ID CO0118010) for the last 3 years. Checked 2026-10-07.
| Rule | Type | Since | Status |
|---|---|---|---|
| Surface Water Treatment Rule | Missed testing or reporting | 05/01/2025 | Resolved |
Source: U.S. EPA Enforcement and Compliance History Online (ECHO), from the Safe Drinking Water Information System. See EPA's full report.
Recommended filters for CASTLE ROCK
Filters matched to the specific contaminants in CASTLE ROCK's water supply.
Reverse osmosis certified for arsenic (NSF/ANSI 58)
$429-$599Reverse osmosis certified under NSF/ANSI 58 for arsenic is the most reliable home option.
Carbon filter certified for VOCs (NSF/ANSI 53)
$180-$599Activated carbon is effective for disinfection byproducts. Look for NSF/ANSI 53 VOC reduction.
Reverse osmosis certified for radium (NSF/ANSI 58)
$429-$750RO certified for radium 226/228 reduces it; ion-exchange water softeners also reduce radium.
Disclosure: TapWaterSafety earns a commission from purchases made through these links. This does not influence our scoring methodology or filter selection.
All contaminants detected in CASTLE ROCK's tap water
Every contaminant identified, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal. 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 |
|---|---|---|---|---|---|---|---|---|
| Arsenic Heavy metal |
0.348 ppb | 0.004 | 10.0 | 10 | 10 | 0.004 | — | 87× over |
| Haloacetic acids (HAA9) Disinfection byproduct |
3.02 ppb | 0.06 | — | — | — | — | — | 50× over |
| Radium, combined (-226 and -228) Radiological |
2.33 pCi/L | 0.05 | 5.0 | — | — | — | — | 47× over |
| Total trihalomethanes (TTHMs) Disinfection byproduct |
4.54 ppb | 0.15 | 80.0 | 100 | — | — | — | 30× over |
| Bromate Disinfection byproduct |
2.25 ppb | 0.1 | 10.0 | 10 | 10 | 0.1 | — | 23× over |
| Dibromoacetic acid Disinfection byproduct |
0.661 ppb | 0.03 | — | — | — | — | — | 22× over |
| Bromodichloromethane Disinfection byproduct |
1.17 ppb | 0.06 | — | — | — | — | — | 19× over |
| Dibromochloromethane Disinfection byproduct |
1.53 ppb | 0.1 | — | — | — | — | — | 15× over |
| Haloacetic acids (HAA5) Disinfection byproduct |
1.5 ppb | 0.1 | 60.0 | 60 | — | — | — | 15× over |
| Chromium (hexavalent) Heavy metal |
0.254 ppb | 0.02 | — | — | — | — | — | 13× over |
| Dichloroacetic acid Disinfection byproduct |
0.675 ppb | 0.2 | — | — | — | — | — | 3.4× over |
| Chloroform Disinfection byproduct |
1.01 ppb | 0.4 | — | — | — | — | — | 2.5× over |
| Nitrate and nitrite Inorganic |
0.353 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 2.5× over |
| Nitrate Inorganic |
0.241 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 1.7× over |
| Chlorate Disinfection byproduct |
355.0 ppb | 210.0 | — | — | — | — | — | 1.7× over |
| Bromoform Disinfection byproduct |
0.841 ppb | 0.5 | — | — | — | — | — | 1.7× over |
| Uranium Radiological |
0.53 pCi/L | 0.43 | 20.0 | 30 | 30 | 0.43 | — | 1.2× over |
| Trichloroacetic acid Disinfection byproduct |
0.0611 ppb | 0.1 | — | — | — | — | — | Below guideline |
| Barium Heavy metal |
138.4 ppb | 700.0 | 2000.0 | — | 1300 | 2000 | — | Below guideline |
| Selenium Heavy metal |
2.7 ppb | 30.0 | 50.0 | 20 | 40 | 30 | — | Below guideline |
| Manganese Heavy metal |
0.9 ppb | 100.0 | — | 50 | 80 | — | — | Below guideline |
| Molybdenum Other |
0.305 ppb | 40.0 | — | — | — | — | — | Below guideline |
| Monobromoacetic acid Disinfection byproduct |
0.101 ppb | 25.0 | — | — | — | — | — | Below guideline |
| Perfluoropentanoic Acid (PFPeA) PFAS |
0.642 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Perfluorobutanoic Acid (PFBA) PFAS |
0.425 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Strontium Radiological |
0.427 ppb | 1500.0 | — | — | — | — | — | Below guideline |
| Chromium (total) Heavy metal |
1.74 ppb | — | 100.0 | — | — | — | — | Below guideline |
| Fluoride Inorganic |
0.762 ppm | — | 4.0 | 1.5 | 1.5 | — | — | Below guideline |
| Lithium Other |
17.6 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, California OEHHA PHGs, EWG Tap Water Database.
Treatment plant contact info
For service issues, water quality concerns, or to request a Consumer Confidence Report from CASTLE ROCK TOWN OF.