Tap Water Quality Report
Tap water quality in ONTARIO, California
Tap water in ONTARIO, California receives a grade of F (55/100) from TapWaterSafety.org. It's served by ONTARIO MUNICIPAL UTILITIES COMPANY. The most significant water quality concerns are: PFAS contamination; Haloacetic acids (HAA5) significantly above health guideline; Haloacetic acids (HAA9) significantly above health guideline; Total trihalomethanes (TTHMs) significantly above health guideline. Data sources: EPA SDWIS, EPA ECHO, EWG Tap Water Database.
What's in ONTARIO's tap water
Top water quality concerns identified by the EPA and Environmental Working Group across the utility serving ONTARIO.
PFAS contamination
Severe concernPerfluorooctanoic acid (PFOA), Perfluorooctane sulfonate (PFOS) detected. PFAS are persistent chemicals linked to cancer and immune effects with no known safe exposure threshold.
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 16.4 ppb, 273x above the EWG health guideline of 0.06 ppb.
Total trihalomethanes (TTHMs) significantly above health guideline
Moderate concernTotal trihalomethanes (TTHMs) detected at 32.3 ppb, 215x above the EWG health guideline of 0.15 ppb.
Recommended filters for ONTARIO
Filters matched to the specific contaminants in ONTARIO's water supply.
Reverse Osmosis or NSF P473 certified carbon
$80-$750Activated carbon and RO are the only technologies proven to remove PFAS at certified levels.
Carbon block (NSF/ANSI 42 + 53)
$40-$750Activated carbon is highly effective for disinfection byproducts like TTHM and HAA5.
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 ONTARIO'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 |
|---|---|---|---|---|---|---|---|---|
| Haloacetic acids (HAA5) Disinfection byproduct |
36.2 ppb | 0.1 | 60.0 | 60 | — | — | — | 362× over |
| Haloacetic acids (HAA9) Disinfection byproduct |
16.4 ppb | 0.06 | — | — | — | — | — | 273× over |
| Total trihalomethanes (TTHMs) Disinfection byproduct |
32.3 ppb | 0.15 | 80.0 | 100 | — | — | — | 215× over |
| Perfluorohexane sulfonate (PFHXS) PFAS |
0.163 ppt | 0.001 | 10.0 | — | — | — | — | 163× over |
| Chromium (hexavalent) Heavy metal |
3.12 ppb | 0.02 | — | — | — | — | — | 156× over |
| Bromodichloromethane Disinfection byproduct |
7.45 ppb | 0.06 | — | — | — | — | — | 124× over |
| Dibromochloromethane Disinfection byproduct |
9.17 ppb | 0.1 | — | — | — | — | — | 92× over |
| Dibromoacetic acid Disinfection byproduct |
1.53 ppb | 0.03 | — | — | — | — | — | 51× over |
| Nitrate and nitrite Inorganic |
2.77 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 20× over |
| Chloroform Disinfection byproduct |
7.17 ppb | 0.4 | — | — | — | — | — | 18× over |
| Bromoform Disinfection byproduct |
8.46 ppb | 0.5 | — | — | — | — | — | 17× over |
| Nitrate Inorganic |
2.28 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 16× over |
| Trichloroacetic acid Disinfection byproduct |
1.55 ppb | 0.1 | — | — | — | — | — | 15× over |
| 1,2-Dibromo-3-chloropropane (DBCP) Other |
0.0151 ppb | 0.0017 | 0.2 | — | — | — | — | 8.9× over |
| Perfluorooctanoic acid (PFOA) PFAS |
0.482 ppt | 0.09 | 4.0 | 100 | 100 | 0.007 | — | 5.4× over |
| Dichloroacetic acid Disinfection byproduct |
0.82 ppb | 0.2 | — | — | — | — | — | 4.1× over |
| Vanadium Other |
9.61 ppb | 21.0 | — | — | — | — | — | Below guideline |
| Perchlorate Disinfection byproduct |
0.454 ppb | 1.0 | — | — | — | — | — | Below guideline |
| Chlorate Disinfection byproduct |
87.8 ppb | 210.0 | — | — | — | — | — | Below guideline |
| Perfluorooctane sulfonate (PFOS) PFAS |
0.072 ppt | 0.3 | 4.0 | 100 | 100 | 1 | — | Below guideline |
| 1,4-Dioxane Semi-volatile organic compound |
0.0263 ppb | 0.35 | — | — | 50 | 1 | — | Below guideline |
| Molybdenum Other |
2.92 ppb | 40.0 | — | — | — | — | — | Below guideline |
| Bromochloromethane Other |
0.00204 ppb | 0.06 | — | — | — | — | — | Below guideline |
| Barium Heavy metal |
7.86 ppb | 700.0 | 2000.0 | — | 1300 | 2000 | — | Below guideline |
| Monobromoacetic acid Disinfection byproduct |
0.118 ppb | 25.0 | — | — | — | — | — | Below guideline |
| Manganese Heavy metal |
0.234 ppb | 100.0 | — | 50 | 80 | — | — | Below guideline |
| Perfluorobutanoic Acid (PFBA) PFAS |
0.307 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Strontium Radiological |
0.316 ppb | 1500.0 | — | — | — | — | — | Below guideline |
| Perfluoropentanoic Acid (PFPeA) PFAS |
0.163 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| 1,1-Dichloroethane Volatile organic compound |
0.000459 ppb | 3.0 | — | — | — | — | — | Below guideline |
| Perfluorohexanoic Acid (PFHxA) PFAS |
0.099 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| 1-Butanol Other |
0.12 ppb | — | — | — | — | — | — | Below guideline |
| Fluoride Inorganic |
0.166 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, 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 ONTARIO MUNICIPAL UTILITIES COMPANY.