What was found in Ontario's water
The level at the city's main supplier, the highest level anywhere in the city, the EPA limit for each, and where every figure comes from.
| Contaminant | Level vs EPA limit | Suppliers | Source |
|---|---|---|---|
| Nitrate | 12000 µg/L 120% of the EPA limit, at the 95th percentile of samples — 10000 µg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019
Highest in the city: 66218 µg/L — CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 2/2 | SYR4 |
| Nitrate-Nitrite | 9840 µg/L 98% of the EPA limit 10000 µg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2017
Highest in the city: 48850 µg/L — CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2017 | 2/2 | SYR4 |
| Nitrite | 4525 µg/L 453% of the EPA limit, at the 95th percentile of samples — 1000 µg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 2/2 | SYR4 |
| Fluoride | 400 µg/L 10% of the EPA limit 4000 µg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019
Highest in the city: 900 µg/L — CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 2/2 | SYR4 |
| Barium | 139.5 µg/L 7% of the EPA limit 2000 µg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019
Highest in the city: 290 µg/L — CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 2/2 | SYR4 |
| TTHM | 71.5 µg/L 89% of the EPA limit 80 µg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 2/2 | SYR4 |
| Total Haloacetic Acids (HAA5) | 31.5 µg/L 53% of the EPA limit 60 µg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 2/2 | SYR4 |
| Trichloroethylene | 28 µg/L 560% of the EPA limit, at the 95th percentile of samples — 5 µg/L Highest in the city: CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 1/2 | SYR4 |
| Bromoform | 27.5 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 2/2 | SYR4 |
| Monochloroacetic Acid | 27 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 2/2 | SYR4 |
| Combined Uranium | 25.7919 µg/L 86% of the EPA limit 30 µg/L Highest in the city: CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 1/2 | SYR4 |
| Dibromochloromethane | 25 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 2/2 | SYR4 |
| Bromodichloromethane | 20.15 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 2/2 | SYR4 |
| Chloroform | 15 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 1/2 | SYR4 |
| Arsenic | 2.39 µg/L 24% of the EPA limit 10 µg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019
Highest in the city: 11 µg/L — CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 2/2 | SYR4 |
| Dibromoacetic Acid | 10.805 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 1/2 | SYR4 |
| Selenium | 9.09 µg/L 18% of the EPA limit 50 µg/L Highest in the city: CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 1/2 | SYR4 |
| Chromium | 7.45 µg/L 7.5% of the EPA limit 100 µg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 2/2 | SYR4 |
| Monobromoacetic Acid | 7.16 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 1/2 | SYR4 |
| Dichloroacetic Acid | 5.405 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 1/2 | SYR4 |
| Trichloroacetic Acid | 4.205 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 1/2 | SYR4 |
| Copper | 3.83 µg/L 0.3% of the EPA limit 1300 µg/L Highest in the city: CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 1/2 | SYR4 |
| cis-1,2-Dichloroethylene | 1.3 µg/L 1.9% of the EPA limit 70 µg/L Highest in the city: CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 1/2 | SYR4 |
| Dichloromethane | 1.1 µg/L 22% of the EPA limit 5 µg/L Highest in the city: CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 1/2 | SYR4 |
| Lead | 0.8000 µg/L 5.3% of the EPA limit 15 µg/L Highest in the city: CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 1/2 | SYR4 |
| 1,1-Dichloroethylene | 0.6335 µg/L 9% of the EPA limit 7 µg/L Highest in the city: CHINO BASIN DESALTER AUTH. - DESALTER 1 · 0 people · 2019 | 1/2 | SYR4 |
| 1,2-DIBROMO-3-CHLOROPROPANE | 0.1200 µg/L 60% of the EPA limit 0.2000 µg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 2/2 | SYR4 |
| PFOA | 0.0300 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2024 | 1/2 | UCMR-5 |
| Ethylene Dibromide | 0.0210 µg/L 42% of the EPA limit 0.0500 µg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2019 | 1/2 | SYR4 |
| Pfhxa | 0.0071 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2024 | 1/2 | UCMR-5 |
| Pfpea | 0.0067 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2024 | 1/2 | UCMR-5 |
| Pfba | 0.0064 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2024 | 1/2 | UCMR-5 |
| PFOS | 0.0052 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2024 | 1/2 | UCMR-5 |
| PFHXS | 0.0042 µg/L No EPA limit set Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2024 | 1/2 | UCMR-5 |
| Lead | 0.00060 mg/L 4% of the EPA limit 0.0150 mg/L Main supplier: ONTARIO MUNICIPAL UTILITIES COMPANY · 185,010 people · 2024 | 1/2 | LCR |
Each bar shows the measured level as a share of the EPA limit: green is
well under, amber is close to it, red is over. For lead and copper the
limit applies to exactly the 90th-percentile figure shown, so red there
means a real exceedance. For everything else the limit applies to a
running annual average while the figure is the 95th percentile of the
system's samples — over 100% is worth reading, but is not by itself a
violation.
Formal violations are listed separately.
These are the utilities' own EPA-reported results, not a city-wide
average. A detection means the lab measured the
substance — it isn't the same as exceeding a legal limit. Hover a source
tag to see the EPA program and years behind each figure.
Water suppliers serving Ontario
| Supplier | Population served |
|---|---|
| ONTARIO MUNICIPAL UTILITIES COMPANY | 185,010 |
| CHINO BASIN DESALTER AUTH. - DESALTER 1 | 0 |
Frequently asked questions about Ontario tap water
Is Ontario tap water safe to drink?
EPA testing detected 35 contaminants in the water serving Ontario. A detection isn't the same as a violation — most detected levels are within federal limits. Check the level and source for each contaminant above, and your utility's annual Consumer Confidence Report for the official compliance status.
How many water suppliers serve Ontario?
2 public water suppliers report drinking-water monitoring for Ontario, California to the EPA. Each is listed above with its population served.
What contaminants are in Ontario's water?
The contaminants EPA monitoring detected in Ontario include Nitrate, Nitrate-Nitrite, Nitrite, Fluoride, Barium. The full list, with the level at the main supplier and the data source, is in the table above.
Where does this data come from?
Every figure is official EPA drinking-water monitoring — the Lead & Copper Rule, the UCMR-5 nationwide testing program, and the EPA Six-Year Review — not our own testing. Each number is labelled with its source and period.