Tap WaterIndex

← California

Tap water quality report

Ontario, CA

EPA monitoring detected 35 contaminants across the 2 water suppliers serving Ontario. A detection doesn't automatically mean the water is unsafe — see the highest level found for each below, with its EPA source and period.

2
water suppliers
185,010
people served
35
contaminants found
California rankings Lead in California PFAS in California

What was found in Ontario's water

The highest level seen across the city's suppliers, the EPA limit for each, and where the figure comes from.

ContaminantLevel vs EPA limitSuppliersSource
Nitrate
135000 µg/L 1350%
of the EPA limit, in the worst sample — 10000 µg/L
 2/2 SYR4
Nitrate-Nitrite
49000 µg/L 490%
of the EPA limit, in the worst sample — 10000 µg/L
 2/2 SYR4
Nitrite
4900 µg/L 490%
of the EPA limit, in the worst sample — 1000 µg/L
 2/2 SYR4
Fluoride
1300 µg/L 33%
of the EPA limit 4000 µg/L
 2/2 SYR4
Barium
330 µg/L 17%
of the EPA limit 2000 µg/L
 2/2 SYR4
Chromium
89 µg/L 89%
of the EPA limit 100 µg/L
 2/2 SYR4
TTHM
77 µg/L 96%
of the EPA limit 80 µg/L
 2/2 SYR4
Total Haloacetic Acids (HAA5)
43 µg/L 72%
of the EPA limit 60 µg/L
 2/2 SYR4
Combined Uranium
36.803 µg/L 123%
of the EPA limit, in the worst sample — 30 µg/L
 1/2 SYR4
Trichloroethylene
35 µg/L 700%
of the EPA limit, in the worst sample — 5 µg/L
 1/2 SYR4
Monochloroacetic Acid
31 µg/L
No EPA limit set
 2/2 SYR4
Chloroform
30 µg/L
No EPA limit set
 1/2 SYR4
Bromoform
29 µg/L
No EPA limit set
 2/2 SYR4
Dibromochloromethane
28 µg/L
No EPA limit set
 2/2 SYR4
Bromodichloromethane
23 µg/L
No EPA limit set
 2/2 SYR4
Copper
16.7 µg/L 1.3%
of the EPA limit 1300 µg/L
 1/2 SYR4
Arsenic
13 µg/L 130%
of the EPA limit, in the worst sample — 10 µg/L
 2/2 SYR4
Dibromoacetic Acid
13 µg/L
No EPA limit set
 1/2 SYR4
Selenium
9.8 µg/L 20%
of the EPA limit 50 µg/L
 1/2 SYR4
Dichloroacetic Acid
7.8 µg/L
No EPA limit set
 1/2 SYR4
Monobromoacetic Acid
7.8 µg/L
No EPA limit set
 1/2 SYR4
Trichloroacetic Acid
5.6 µg/L
No EPA limit set
 1/2 SYR4
cis-1,2-Dichloroethylene
1.5 µg/L 2.1%
of the EPA limit 70 µg/L
 1/2 SYR4
Dichloromethane
1.1 µg/L 22%
of the EPA limit 5 µg/L
 1/2 SYR4
Lead
0.8000 µg/L 5.3%
of the EPA limit 15 µg/L
 1/2 SYR4
1,1-Dichloroethylene
0.6400 µg/L 9.1%
of the EPA limit 7 µg/L
 1/2 SYR4
1,2-DIBROMO-3-CHLOROPROPANE
0.1600 µg/L 80%
of the EPA limit 0.2000 µg/L
 2/2 SYR4
PFOA
0.0300 µg/L
No EPA limit set
 1/2 UCMR-5
Ethylene Dibromide
0.0210 µg/L 42%
of the EPA limit 0.0500 µg/L
 1/2 SYR4
Pfhxa
0.0071 µg/L
No EPA limit set
 1/2 UCMR-5
Pfpea
0.0067 µg/L
No EPA limit set
 1/2 UCMR-5
Pfba
0.0064 µg/L
No EPA limit set
 1/2 UCMR-5
PFOS
0.0052 µg/L
No EPA limit set
 1/2 UCMR-5
PFHXS
0.0042 µg/L
No EPA limit set
 1/2 UCMR-5
Lead
0.00060 mg/L 4%
of the EPA limit 0.0150 mg/L
 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 single worst sample on record — 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

SupplierPopulation 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 highest level found 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.