Diamond Bar, CA Water Safety: 63/100 (2026)
1 ZIP code · 3 water systems · Updated 2026-06-03
In recent monitoring cycles, Diamond Bar tap water shows a mixed record for CA — several systems have documented violations alongside areas with clean compliance histories.
How Diamond Bar Compares
Data: EPA SDWIS Last verified: 2026-06-03
What You Should Know About Diamond Bar Water
- Homes built before 1986: 77% — older plumbing may contain lead solder.
- Estimated remediation: $2,100 per household.
- CDC health risk index: 10.71.
Who Supplies Your Water in Diamond Bar
3 independent water providers serve Diamond Bar, CA — 3 systems appear in federal records.
Overview
We track water quality and home safety data for 1 ZIP code in Diamond Bar, California (population ~44,779), covering 3 community water systems serving approximately 155,601 people region-wide.
No EPA violations recorded across any ZIP codes in Diamond Bar — an excellent indicator of water quality.
Home Safety Score
Average Home Safety Score for Diamond Bar: C (63/100)
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
Diamond Bar water systems draw from: Surface water.
Lead & Copper
- Lead data: not yet available for Diamond Bar
- 0 ZIP codes exceed the EPA lead action level
Radon Risk
Dominant radon zone: Zone 2 (Moderate Risk)
The EPA recommends testing homes in Zone 1 and Zone 2 areas for radon.
Areas with No Violations
| ZIP Code | Safety Score | System | Population |
|---|---|---|---|
| 91765 | C | WALNUT VALLEY WATER DISTRICT | 100,941 |
All ZIP Codes in Diamond Bar
- 91765 [C]
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.
Health Outcomes in Diamond Bar
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
Housing & Infrastructure in Diamond Bar
With 77% 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
Heavily weighted toward older construction, Diamond Bar's housing stock carries a median build year of 1971. That profile puts a majority of homes in the era when lead-soldered copper plumbing was standard practice.
Over half of homes in Diamond Bar 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.
Cost Context: What Remediation Means for Diamond Bar Homeowners
The household financial picture for Diamond Bar homeowners is proportionally favorable — addressing documented issues claims a small slice of equity, and the cost-to-value ratio puts this area well within the manageable tier.
Remediation costs in Diamond Bar are relatively low compared to home values. The $1,100–$3,400 estimated range is a small fraction of median property value. Home values are 19% above the California average.
Lead Exposure Risk for Children in Diamond Bar
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.
Older stock in Diamond Bar represents 77% of the inventory, and citywide monitoring runs at or above the federal action level — making an in-home read a standard household-level step.
Sources: EPA Lead and Copper Rule, U.S. Census Bureau ACS, CDC childhood lead poisoning prevention guidelines.
Flood & Climate Risk in Diamond Bar
Within the NFIP's national dataset, Diamond Bar falls in moderate-exposure territory — 7 documented incidents spanning multiple decades, with 100% of local ZIP codes sitting inside FEMA flood boundaries. That combination warrants inclusion in any thorough local water quality review.
Diamond Bar has a moderate flood history with 7 FEMA claims averaging $972 per payout. 100% 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>$2,100</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.
What You Can Do in Diamond Bar
- Test your water at home. City-level data shows averages — your tap may differ. NSF-certified test kits cost $20-40 and give results in days.
- Install a certified water filter. An NSF-certified pitcher or under-sink filter removes most common contaminants.
- Check your home's plumbing. With 77% of homes built before 1986, lead solder is a real possibility.
Deep Dive Reports
Detailed analysis for Diamond Bar, CA