A92/100
Ontario Tap Water Quality: Is It Safe to Drink? (2026 Report)
Serving 185,010 residents · California
What's In Ontario's Tap Water?
76
Contaminants Tested
0
Exceed EPA Limits
1
Above EPA Goals
1 contaminant above EPA health goals
| Contaminant | Detected | Limit (MCL) | Status |
|---|---|---|---|
Lead (90th percentile) | < 0.001 mg/L | 0.015 mg/L | Above Goal |
EPA Violation History
No violations in the past 5 years
Full EPA compliance since 1993.
Understanding violation severity
Tier 1Urgent health risk. Utility must notify all customers within 24 hours.Tier 2Important health or treatment issue. Customers notified within 30 days.Tier 3Administrative or monitoring issue. Reported in the annual water quality report.
Source: EPA Safe Drinking Water Information System (SDWIS) · Updated quarterly
Water Utility Details
ONTARIO MUNICIPAL UTILITIES COMPANY
Population Served
185,010
Water Source
Purchased Surface Water
System ID
CA3610034
Frequently Asked Questions About Ontario Water
Is Ontario tap water safe to drink?
Ontario, California tap water receives a grade of A (92/100), which is considered excellent. Out of 76 contaminants tested, none exceed EPA maximum contaminant levels (MCLs) and 1 exceed health guidelines (MCLGs). While the water meets federal standards, some residents may still choose to use a filter for additional peace of mind.
What contaminants are in Ontario's water?
Of the 76 contaminants tested in Ontario's water supply, the most notable include Lead (90th percentile). No contaminants exceed EPA legal limits. 1 contaminant(s) exceed EPA health goals (MCLGs), which are non-enforceable targets set at levels with no known health risk.
Does Ontario have any water quality violations?
Yes, Ontario has 1 EPA violation(s) on record, with the most recent in 1993. Violation types include TT. 1 of these are health-based violations, which are the most serious category.
Do I need a water filter in Ontario?
Ontario water meets EPA standards, so a filter is not strictly necessary. However, some residents prefer the added security of a water filter. EPA health goals (MCLGs) are stricter than legal limits and are set at levels with zero expected health risk. 1 contaminant(s) exceed these stricter goals.
Where does Ontario's tap water come from?
Ontario's drinking water is sourced from purchased surface water and supplied by ONTARIO MUNICIPAL UTILITIES COMPANY. The system serves approximately 185,010 people. Surface water sources include rivers, lakes, and reservoirs.
How often is Ontario's water tested?
Under the Safe Drinking Water Act (SDWA), water utilities are required to regularly test for over 90 contaminants. Testing frequency varies by contaminant — some are tested monthly, others quarterly or annually. Ontario's water systems must report results to the EPA and publish an annual Consumer Confidence Report (CCR). The data on this page reflects the latest available EPA testing data.
How does Ontario's water compare to other cities in California?
Ontario's water quality score of 92/100 earns a grade of A, which is considered excellent. This places Ontario among the better-performing water systems in California. Visit our California state page to see how all cities in the state compare.
What should I do if I'm concerned about Ontario's water quality?
If you have concerns about Ontario's tap water, consider these steps: (1) Request your utility's annual Consumer Confidence Report for detailed local data. (2) Get your water independently tested through a state-certified laboratory. (3) Consider an NSF-certified water filter rated for the contaminants found in your area. (4) Contact your water utility (ONTARIO MUNICIPAL UTILITIES COMPANY) with specific questions. (5) Report water quality issues to your state drinking water program or the EPA Safe Drinking Water Hotline at 800-426-4791.