Ontario, CA Water Safety: 82/100 (2026)
5 ZIP codes · 6 water systems · Updated 2026-06-03
Water systems in Ontario, CA serve households with few reported safety events.
How Ontario Compares
Data: EPA SDWIS Last verified: 2026-06-03
Water Quality Map: Ontario, CA
Each dot represents a ZIP code. Color indicates water quality grade. Tap a dot for details.
Score Distribution
Distribution of water safety grades across Ontario.
Ontario Water: The Quick Version
- Average lead level: 0.0006 mg/L.
- Homes built before 1986: 65% — older plumbing may contain lead solder.
- Estimated remediation: $1,480 per household.
- CDC health risk index: 11.58.
Water Systems Serving Ontario
Federal drinking water records identify 6 systems in Ontario, CA. The leading 3 providers serve the largest share of residential connections, each operating as a separate entity with its own rate authority, infrastructure management, and EPA compliance obligations — so service conditions are not uniform city-wide.
Overview
We track water quality and home safety data for 5 ZIP codes in Ontario, California (population ~181,574), covering 6 community water systems serving approximately 538,531 people region-wide.
No EPA violations recorded across any ZIP codes in Ontario — an excellent indicator of water quality.
Home Safety Score
Average Home Safety Score for Ontario: B (82/100)
The score combines three factors:
| Factor | What It Measures |
|---|---|
| Water Quality | EPA violations and compliance history |
| Lead Levels | 90th percentile lead concentration vs EPA action level |
| Radon Risk | EPA radon zone classification |
Water Sources
Ontario water systems draw from: Groundwater, Surface water.
Lead & Copper
- Average lead level (90th percentile): 0.0006 mg/L (EPA action level: 0.015 mg/L)
- 0 ZIP codes exceed the EPA lead action level
Radon Risk
Dominant radon zone: Zone 2 (Moderate Risk)
- Zone 1 (High): 0 ZIP codes
- Zone 2 (Moderate): 5 ZIP codes
- Zone 3 (Low): 0 ZIP codes
The EPA recommends testing homes in Zone 1 and Zone 2 areas for radon.
Areas with No Violations
| ZIP Code | Safety Score | System | Population |
|---|---|---|---|
| 91758 | B | Ontario Municipal Utilities Company | 185,010 |
| 91761 | B | Ontario Municipal Utilities Company | 185,010 |
| 91762 | B | Ontario Municipal Utilities Company | 185,010 |
| 91764 | B | Ontario Municipal Utilities Company | 185,010 |
| 91798 | B | Ontario Municipal Utilities Company | 185,010 |
All ZIP Codes in Ontario
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Lead/copper: EPA Lead and Copper Rule sampling data
- Radon: EPA Map of Radon Zones
Updated daily.
CDC Health Data for Ontario
Source: CDC PLACES (County-level estimates). Water contamination can correlate with respiratory and chronic health conditions.
Compared to National Average
Vertical line = national average. ■ Above national · ■ Below national
How Old Is Ontario's Housing Stock?
With 65% of homes built before 1986, lead solder in plumbing is a potential concern. The EPA banned lead solder in 1986, but many older homes retain original plumbing.
Source: U.S. Census Bureau American Community Survey (ACS).
Housing Age Profile
Ontario's housing stock is predominantly older, with a median build year of 1979 that reflects decades of construction before federal plumbing standards were tightened. The 1986 ban on lead solder and the pre-1970 era of lead service lines are both relevant benchmarks here — a significant share of the residential inventory predates one or both of those cutoffs, creating an elevated baseline for plumbing-related lead risk that aggregate water quality data may not fully reflect at the household level.
Over half of homes in Ontario were built before 1986, when lead solder was banned. Older plumbing may leach lead into drinking water, especially with corrosive water chemistry.
Source: U.S. Census Bureau ACS B25034.
Ontario: Remediation Cost in Perspective
Placing remediation in the context of Ontario's property market, the equity share is low — most homeowners here are weighing a financial commitment that fits comfortably within routine property planning, far from the threshold where remediation becomes a material equity decision rather than a standard upkeep consideration.
Remediation costs in Ontario are relatively low compared to home values. The $720–$2,360 estimated range is a small fraction of median property value. Home values are 23% below the California average.
Protecting Children from Lead in Ontario
Why children are most at risk: The CDC states there is no safe level of lead exposure for children. Children under 6 absorb lead more readily than adults, and even low levels can cause developmental delays, learning difficulties, and behavioral problems.
Before the federal solder ban, lead solder was a routine plumbing material, and 65% of the Ontario inventory was built in that earlier era — a share large enough to move household-level reads onto the standard list.
Sources: EPA Lead and Copper Rule, U.S. Census Bureau ACS, CDC childhood lead poisoning prevention guidelines.
Climate-Related Water Risk for Ontario
Multiple flood events have been recorded for Ontario through the NFIP — 21 claims in total, with 40% of ZIP codes in FEMA-designated zones — pointing to a flood exposure profile that merits inclusion in a water quality assessment without reaching high-severity planning territory.
Ontario has a moderate flood history with 21 FEMA claims averaging $1,492 per payout. 40% of ZIP codes fall within FEMA flood zones. Flood events can contaminate drinking water and overwhelm treatment systems.
How flooding affects water quality: Flood events can introduce sewage, agricultural runoff, and industrial chemicals into water supplies. Even after floodwaters recede, contamination can persist in wells and aging infrastructure. Flood damage can add significantly to the estimated <strong>$1,480</strong> remediation cost per household.
Residents in flood-prone areas should consider flood insurance even outside FEMA zones — over 25% of flood claims come from low-to-moderate risk areas. After any flood event, test your water before drinking.
Source: FEMA National Flood Insurance Program (NFIP) claims data, FEMA flood zone designations.
Deep Dive Reports
Detailed analysis for Ontario, CA