Tap Water Results

Is Diamond Bar, CA tap water safe?

Data: U.S. EPA · How we read the data · How we check it

Summary

No federal limits exceeded in EPA data for Walnut Valley Water District.

2 public water systems serve parts of Diamond Bar. The largest, Walnut Valley Water District, serves 100,941 people. Your water bill names your system.

Largest system

Walnut Valley Water District

100,941 people · Purchased surface water · EPA ID CA1910234

Buys treated water from Three Valleys Municipal Water District, Metropolitan Water District of SO. Cal..

PFASHighest averageLimitStatus
PFOA
Not detected
–4 pptNot detected
PFOS
Not detected
–4 pptNot detected
PFHxS
Not detected
–10 pptNot detected
PFNA
Not detected
–10 pptNot detected
HFPO-DA (GenX)
Not detected
–10 pptNot detected

ppt = parts per trillion. "Highest average" is the highest average at any of the system's entry points, the way EPA compares results with the limits.

Lead: 0 ppb at the 90th percentile (Dec 2024, and 9 in 10 homes sampled were at or below it) Below action level
Health-based violations since 2016: 0

Full Walnut Valley Water District results

Across California, 129 of 691 water systems EPA tested had PFAS above a 2024 federal limit, and 26 systems were above the lead action level in results from the last five years. California results.

Diamond Bar homes and lead pipes

50%
of homes built before 1980 (California 56%, US 50%)
1%
built before 1950 (California 14%)
23%
of households rent (California 44%)

Lead service lines and lead solder were allowed until 1986, so homes from before then are the ones to check. How to check your own line.

Housing: Census American Community Survey 2020–2024 5-year estimates for Diamond Bar city (tables B25034, B25003). Estimates for small places have a margin of error.

Other water systems serving Diamond Bar

How nearby cities compare

CityMain water systemPFASLead (90th pct.)
Walnut 3 mi
Suburban Water Systems-San Jose
Suburban Water Systems-San JoseNone above limits0 ppb
Pomona 5 mi
City of Pomona Water Dept.
City of Pomona Water Dept.Above limit2.1 ppb
Brea 6 mi
Yorba Linda Water District
Yorba Linda Water DistrictNone above limits0 ppb
West Covina 6 mi
San Gabriel Valley Water Company – El Monte
San Gabriel Valley Water Company – El MonteNone above limits0 ppb
Chino Hills 7 mi
City of Chino Hills
City of Chino HillsNone above limits0 ppb
Covina 7 mi
Suburban Water Systems-San Jose
Suburban Water Systems-San JoseNone above limits0 ppb
Diamond Bar ZIP codes (1)
  • 91765

Questions

Is Diamond Bar tap water safe to drink?

Walnut Valley Water District has had no health-based violations since 2016. Utility data can't show lead from your own pipes: if your home was built before 1986, test your tap. Your utility's annual Consumer Confidence Report is the official summary.

Who supplies water in Diamond Bar, CA?

2 public water systems serve parts of Diamond Bar. The largest is Walnut Valley Water District (100,941 people). Your water bill names your system. The EPA ID is also on your utility's Consumer Confidence Report.

Does Diamond Bar tap water have PFAS?

None detected above EPA's reporting limits. Walnut Valley Water District had no PFAS detected in EPA's 2023–2025 testing. "Not detected" means below the reporting limit (about 2 to 20 ppt), not proven zero.

Do Diamond Bar homes have lead pipes?

Census estimates put 50% of Diamond Bar homes as built before 1980 (California: 56%). Lead service lines and lead solder were allowed until 1986, so older homes are more likely to have them. Walnut Valley Water District's service line inventory says what your line is made of. The only way to know for your home is to check the line where it enters the house and test your tap.

Source: U.S. EPA drinking water records and PFAS testing (UCMR 5). How we read the data.