Water Quality Report · Updated October 07, 2026
CASTLE ROCK TOWN OF
CASTLE ROCK TOWN OF delivers tap water graded B (75/100) by TapWaterSafety.org. The utility serves approximately 106,822 residents in CASTLE ROCK, Colorado using surface water. 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. For questions, the utility can be reached at 720-733-6041.
Is CASTLE ROCK tap water safe to drink?
CASTLE ROCK TOWN OF delivers tap water that earns a grade of B (75/100) from TapWaterSafety.org — a good rating, with only minor concerns relative to health-based guidelines.
The utility serves 106,822 residents in CASTLE ROCK, drawing from surface water.
Public testing data identifies 17 contaminants in this water above EWG's health-based guidelines, including: Arsenic, Haloacetic acids (HAA9), Radium, combined (-226 and -228), Total trihalomethanes (TTHMs), Bromate, Dibromoacetic acid, Bromodichloromethane, Dibromochloromethane, Haloacetic acids (HAA5), Chromium (hexavalent), Dichloroacetic acid, Chloroform, Nitrate and nitrite, Nitrate, Chlorate, Bromoform, Uranium. For most residents, a properly certified home filter at the kitchen tap is the most cost-effective way to reduce exposure to whatever's in your water. See our filter recommendations below, matched specifically to this utility's contaminant profile.
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.
Quick actions for CASTLE ROCK residents
Top concerns in this water
Based on the most recent EPA and EWG data, these are the most significant water quality issues for CASTLE ROCK TOWN OF.
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.
Contact CASTLE ROCK TOWN OF
Reach the utility directly for service issues, water quality concerns, or to request your Consumer Confidence Report.
General Contact
Treatment Plant
Recommended water filters for CASTLE ROCK
Filters matched to the specific contaminants in this 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.
Score breakdown
This utility's overall score of 75/100 breaks down across five weighted components. Read the full methodology →
Contaminants detected — international standards comparison
Every contaminant detected, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal (the strictest US benchmark). 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 (4th ed.), California OEHHA PHGs, EWG Tap Water Database.
CASTLE ROCK TOWN OF service area
This water system serves 1 community in Douglas County, Colorado. Click any city for its dedicated tap water quality page.
Find the right filter for CASTLE ROCK water
Browse filter categories by water-quality concern. Each option below is NSF-certified for the matched contaminant type.