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 2019 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).

Lab Testing


Call our Water Quality Hotline at 925-688-8156 or send us an email.

Recent Water Quality Results

  1. SubstanceMaximum Contaminant LevelMost Recent ResultDateSource
    Arsenic0.01 mg/L< 0.002 mg/L7/5/2022BCWO Annual
    ChlorideNo MCL109 mg/L11/15/2022BCWO
    Chlorine Residual4.0 mg/L3.0 mg/L11/15/2022BCWO
    Total Coliforms>5% positive0% positive11/2022Last DDW Report
    HardnessNo MCL125 mg/L11/15/2022BCWO
    HardnessNo MCL7.3 grains/gallon11/15/2022BCWO


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.

mg/L (milligrams per liter)
ppm (parts per million)
1 second in 11.5 days


R/BCWO = Randall-Bold Water Treatment Plant Clearwell Out

BCWO = Bollman Water Treatment Plant Clearwell Out

DDW = Division of Drinking Water