Water Quality Data

Your water is regularly tested for more than 120 chemicals and other substances, as well as radioactivity. The table below provides detailed information about the water that comes from your tap after it is treated (treated water) and before it is treated (raw water). The substances shown are ones that our customers have the most questions about.

You can also view the latest Annual Water Quality Report, which lists the annual results for these substances as well as many others.

For a comprehensive list of contaminants that we test for and have not been detected in our water supply, see our 2018 Contaminants Not Detected List (PDF).

Also, the United States Environmental Protection Agency has additional contaminant list information about the fourth Unregulated Contaminant Monitoring Rule (UCMR 4). For general background information, see their UCMR Basic Information Fact Sheet (PDF).

Questions? Call our Water Quality Hotline at 925-688-8156 or email us.

Lab Testing

Recent Water Quality Results

Substance Maximum Contaminant Level* Most Recent Result Date Source
Arsenic 0.01 mg/L < 0.002 mg/L 7/08/2019 BCWO annual
Chloride No MCL (65 mg/L CCWD Internal Action Level) 33 mg/L 7/08/2019 BCWO
Chlorine Residual 4.0 mg/L 3.7 mg/L 7/30/2019 BCWO
Mercury 0.002 mg/L <0.0002 mg/L 7/08/2019 BCWO annual
Radon ** 300 pci/L <100pci/L 3/2019 Mallard Res; triennial
Total Coliforms >5% positive 0% positive 7/2019 Last DDW report
Hardness No MCL 60 mg/L 7/08/2019 BCWO
Hardness No MCL 3.5 grains/gallon 7/08/2019 BCWO

*Maximum Contaminant Level (MCL): The highest level of a contaminant that is allowed in drinking water based on health risk coupled with economic and technical feasibility for control/treatment.                

**untreated (raw) water sample

pci/L = picocuries per liter

mg/L = milligrams per liter = parts per million

ug/L = micrograms per liter = parts per billion


R/BCWO = Randall-Bold Clearwell Out

BCWO = Bollman Clearwell Out

DDW = Division of Drinking Water