Hexavalent Chromium in Drinking Water Sources: Sampling Results

Recent Monitoring and Analytical Information

  • US EPA Recommendations: US EPA's January 2011 recommendations for enhanced hexavalent chromium monitoring refer public water systems to California laboratories, specifically to laboratories certified by the Environmental Laboratory Accreditation Program (ELAP). US EPA mentions that laboratories identified under Field of Accreditation 103 (FOA 103) can be contacted to see if they are certified for CA subgroup code 103.310, which is specific to EPA Method 218.6 for hexavalent chromium. To assist public water systems that may seek California laboratories, a list is available on the ELAP website.
  • Detection Limit for Purposes of Reporting: In 2014, California established a 10-μg/L hexavalent chromium MCL, which became effective July 1, 2014. As part of the MCL regulatory process, California established a detection limit for purposes of reporting of 1-μg/L for monitoring of hexavalent chromium in drinking water. The hexavalent chromium MCL was repealed in 2017. 
  • Holding Times and Sample Preservation: We concur with US EPA's maximum holding time of 14 days for properly preserved drinking water samples. At this time, we recommend that samples be preserved in the field with one of the buffers described in EPA Method 218.7
  • EPA Methods: ELAP certifies laboratories for EPA Method 218.6 and 218.7.
  • Sampling Results

    Unregulated Chemical Monitoring for Hexavalent Chromium

    In 2001, the California Department of Public Health CDPH (then the California Department of Health Services, DHS) adopted a regulation that added hexavalent chromium to the list of unregulated chemicals for which monitoring is required (UCMR). The analytical methods associated with the UCMR are here.

    Of the ~4,400 community systems and non-transient non-community systems that have ~12,000 drinking water sources, those that are vulnerable to contamination  were subject to UCMR regulations. Systems with fewer than 150 service connections may be exempted from the monitoring requirement. Results of UCMR monitoring from over 7,000 drinking water sources showed hexavalent chromium at or above the 1-μg/L DLR in about one-third of them.

    The monitoring data that were collected as a result of the UCMR regulation enabled us to determine the extent to which hexavalent chromium exists within drinking water supplies, and at what concentrations it exists. This information assisted evaluation of drinking water treatment costs for hexavalent chromium when developing a hexavalent chromium maximum contaminant level (i.e., drinking water standard).

    The monitoring for hexavalent chromium under the UCMR regulations was to have been completed by December 31, 2002, and the UCMR regulations were repealed in October 2007. However, some water systems continued to monitor their sources and submit their findings.


    The Division of Drinking Water's water quality database's reported findings of hexavalent chromium from 2012 to February 2022 are presented below; sources with no detections are excluded. A summary of the peak concentrations is presented in Table 1. Detections included in the accompanying spreadsheet should not be considered to reflect hexavalent chromium in drinking water served to customers, since water from the listed sources may be blended, treated, or not used to provide drinking water. For more information about the quality of specific drinking water supplies, see public water systems' annual Consumer Confidence Reports.

    The water quality monitoring database is available here.

    Map of source occurrence data for hexavalent chromium

    Map of hexavalent chromium data

    Table 1. Hexavalent chromium average drinking water source concentration (2012 - 2022).

    Average Source Concentration (μg/L)

    No. of Sources

    % of Detections

    ≥ 1 and ≤ 5



     > 5 and ≤ 10



     > 10 and ≤ 20



    > 20 and ≤ 30



    > 30 and ≤ 40



    > 41 and ≤ 50



    > 50






    1. Data are extracted from community water system monitoring results from 2012 through February, 2022 (Excel).
    2. "Sources" are active, standby, and pending sources reporting more than a single detection of hexavalent chromium. Data may include both raw and treated sources, distribution systems, blending reservoirs, and other sampled entities. This table does not include inactive sources, abandoned or destroyed wells, agricultural wells, monitoring wells, or more than one representation of the same source (e.g., a source with both raw and treated entries is counted a single source). 
    3. A number of sources may have been screened using a 1-μg/L reporting limit for total chromium (PDF). If total chromium was below the screening level, specific analysis for hexavalent chromium was not required.

    Average source concentrations of hexavalent chromium were reported in the greatest numbers in the following counties (see Notes in Table 1):

    • Concentrations ≥ 1 and ≤ 5 μg/L: 6,850 sources in 58 counties, including San Bernardino (650 sources), Los Angeles (697), Fresno (448), Sacramento (195), Riverside (386), Kern (363), Monterey (302), Sonoma (245), and Tulare (311)
    • Concentrations > 5 and ≤ 10 μg/L: 603 sources in 38 counties, including Los Angeles (111), Monterey (35), Sacramento (55), San Bernardino (74, Riverside (67), San Joaquin (40), Stanislaus (42), and Kern (31)
    • Concentrations > 10 and ≤ 20 μg/L: 263 sources in 25 counties, including Riverside (73), Los Angeles (35), San Bernardino (22), Yolo (15), Sacramento (13), and Santa Cruz (16), Solano (10)
    • Concentrations > 20 and ≤ 30 μg/L: 45 sources in 15 counties, including Yolo (5), Los Angeles (1), San Bernardino (4), Monterey (7), Merced (5), Solano (4), and Riverside (5)
    • Concentrations > 30 and ≤ 40 μg/L: 13 sources in 6 counties: Merced (7), Los Angeles (1), Santa Barbara (1), San Bernardino (1), and Santa Cruz (2)
    • Concentrations > 41 and ≤ 50 μg/L: 3 sources in 2 counties: Riverside (1) and Yolo (1)
    • Concentrations > 50 μg/L: 3 sources in 2 counties: Los Angeles (2) and Ventura (1)