Water Quality Report · Updated October 07, 2026
GSWC-SAN DIMAS
GSWC-SAN DIMAS delivers tap water graded C (67/100) by TapWaterSafety.org. The utility serves approximately 56,538 residents in SAN DIMAS, California using surface water (purchased). The most significant water quality concerns are: Haloacetic acids (HAA5) significantly above health guideline; Haloacetic acids (HAA9) significantly above health guideline; Total trihalomethanes (TTHMs) significantly above health guideline; Arsenic detected. For questions, the utility can be reached at 760-515-8322.
Is SAN DIMAS tap water safe to drink?
GSWC-SAN DIMAS delivers tap water that earns a grade of C (67/100) from TapWaterSafety.org — an average rating, with several contaminants above health guidelines but generally compliant with US legal limits.
The utility serves 56,538 residents in SAN DIMAS, drawing from surface water (purchased).
Public testing data identifies 15 contaminants in this water above EWG's health-based guidelines, including: Haloacetic acids (HAA5), Haloacetic acids (HAA9), Total trihalomethanes (TTHMs), Bromodichloromethane, Dibromochloromethane, Arsenic, Dibromoacetic acid, Nitrate and nitrite, Nitrate, Dichloroacetic acid, Chloroform, Chromium (hexavalent), Trichloroacetic acid, Uranium, Bromoform. 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 GSWC-SAN DIMAS (system ID CA1910142) for the last 3 years. Checked 2026-10-07.
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 SAN DIMAS residents
Top concerns in this water
Based on the most recent EPA and EWG data, these are the most significant water quality issues for GSWC-SAN DIMAS.
Haloacetic acids (HAA5) significantly above health guideline
Moderate concernHaloacetic acids (HAA5) detected at 36.2 ppb, 362x above the EWG health guideline of 0.1 ppb.
Haloacetic acids (HAA9) significantly above health guideline
Moderate concernHaloacetic acids (HAA9) detected at 15.1 ppb, 251x above the EWG health guideline of 0.06 ppb.
Total trihalomethanes (TTHMs) significantly above health guideline
Moderate concernTotal trihalomethanes (TTHMs) detected at 24.6 ppb, 164x above the EWG health guideline of 0.15 ppb.
Arsenic detected
Moderate concernArsenic detected at 0.267 ppb.
Contact GSWC-SAN DIMAS
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 SAN DIMAS
Filters matched to the specific contaminants in this water supply.
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 arsenic (NSF/ANSI 58)
$429-$599Reverse osmosis certified under NSF/ANSI 58 for arsenic is the most reliable home option.
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 67/100 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 |
|---|---|---|---|---|---|---|---|---|
| Haloacetic acids (HAA5) Disinfection byproduct |
36.2 ppb | 0.1 | 60.0 | 60 | — | — | — | 362× over |
| Haloacetic acids (HAA9) Disinfection byproduct |
15.1 ppb | 0.06 | — | — | — | — | — | 251× over |
| Total trihalomethanes (TTHMs) Disinfection byproduct |
24.6 ppb | 0.15 | 80.0 | 100 | — | — | — | 164× over |
| Bromodichloromethane Disinfection byproduct |
7.19 ppb | 0.06 | — | — | — | — | — | 120× over |
| Dibromochloromethane Disinfection byproduct |
8.35 ppb | 0.1 | — | — | — | — | — | 83× over |
| Arsenic Heavy metal |
0.267 ppb | 0.004 | 10.0 | 10 | 10 | 0.004 | — | 67× over |
| Dibromoacetic acid Disinfection byproduct |
1.74 ppb | 0.03 | — | — | — | — | — | 58× over |
| Nitrate and nitrite Inorganic |
4.7 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 34× over |
| Nitrate Inorganic |
4.34 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 31× over |
| Dichloroacetic acid Disinfection byproduct |
4.95 ppb | 0.2 | — | — | — | — | — | 25× over |
| Chloroform Disinfection byproduct |
6.67 ppb | 0.4 | — | — | — | — | — | 17× over |
| Chromium (hexavalent) Heavy metal |
0.332 ppb | 0.02 | — | — | — | — | — | 17× over |
| Trichloroacetic acid Disinfection byproduct |
1.68 ppb | 0.1 | — | — | — | — | — | 17× over |
| Uranium Radiological |
2.86 pCi/L | 0.43 | 20.0 | 30 | 30 | 0.43 | — | 6.7× over |
| Bromoform Disinfection byproduct |
2.73 ppb | 0.5 | — | — | — | — | — | 5.5× over |
| Chlorate Disinfection byproduct |
73.6 ppb | 210.0 | — | — | — | — | — | Below guideline |
| Vanadium Other |
3.25 ppb | 21.0 | — | — | — | — | — | Below guideline |
| Molybdenum Other |
4.0 ppb | 40.0 | — | — | — | — | — | Below guideline |
| Barium Heavy metal |
68.8 ppb | 700.0 | 2000.0 | — | 1300 | 2000 | — | Below guideline |
| Manganese Heavy metal |
1.7 ppb | 100.0 | — | 50 | 80 | — | — | Below guideline |
| Aluminum Heavy metal |
5.0 ppb | 600.0 | — | 200 | — | 600 | — | Below guideline |
| Monobromoacetic acid Disinfection byproduct |
0.165 ppb | 25.0 | — | — | — | — | — | Below guideline |
| Monochloroacetic acid Disinfection byproduct |
0.255 ppb | 53.0 | — | — | — | — | — | Below guideline |
| Strontium Radiological |
0.634 ppb | 1500.0 | — | — | — | — | — | Below guideline |
| Chlorodifluoromethane Other |
0.0556 ppb | — | — | — | — | — | — | Below guideline |
| Fluoride Inorganic |
0.626 ppm | — | 4.0 | 1.5 | 1.5 | — | — | 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.
GSWC-SAN DIMAS service area
This water system serves 1 community in Los Angeles County, California. Click any city for its dedicated tap water quality page.
Find the right filter for SAN DIMAS water
Browse filter categories by water-quality concern. Each option below is NSF-certified for the matched contaminant type.