Hexavalent Chromium (Chromium-6)


Hexavalent chromium is a heavy metal that has been used in industrial applications and found naturally occurring throughout the environment. While chromium can exist in a nontoxic, trivalent form, the hexavalent form has been shown to be carcinogenic and toxic to the liver (OEHHA, 2011). Hexavalent chromium is among the chemicals known to the state to cause cancer [Title 27, California Code of Regulations, Section 27001], pursuant to California's Safe Drinking Water and Toxic Enforcement Act of 1986 ("Proposition 65").

The State Water Board is required to set MCLs “as close as feasible to the corresponding public health goal [PHG] placing primary emphasis on the protection of public health,” to the extent that it is technologically and economically feasible [Health & Safety Code § 116365(a)]. The PHG for hexavalent chromium (0.02 μg/L) was established in 2011. The rulemaking to establish an MCL (proposed at 10 μg/L) is currently in progress.

Readers interested in the levels of hexavalent chromium in their drinking water may refer to the water systems' annual Consumer Confidence Reports (CCRs). Many CCRs are available from DDW's Drinking Water Watch website, which also includes other information about drinking water quality.


The following sampling results were obtained from laboratories using one of the following ELAP accredited methods:

The Division of Drinking Water's water quality database's reported findings of hexavalent chromium from 2012 to February 2022; sources with no detections are excluded. A summary of the peak concentrations is presented in Table 1. Detections included in the accompanying spreadsheet (linked in Table note #1 below) 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.

Map of source occurrence data for hexavalent chromium
Figure Caption

Map of source occurrence data for hexavalent chromium

Table showing 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).

Average source concentrations of hexavalent chromium from the data above were reported in the greatest numbers in the following counties:

  • 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)

Historical Timeline

Below are significant historical events associated with the development of drinking water regulations for hexavalent chromium:

Total Chromium MCL and Information

Hexavalent chromium has been regulated under the 50-µg/L primary drinking water standard (MCL) for total chromium. California's MCL for total chromium was established in 1977, when we adopted what was then a "National Interim Drinking Water Standard" for chromium. The total chromium MCL was established to address exposures to hexavalent chromium, the more toxic form of chromium. Chromium-3 (trivalent chromium) is a required nutrient.

The US Environmental Protection Agency (EPA) adopted the same 50-µg/L standard tor total chromium, but in 1991 raised the federal MCL to 100 µg/L. California did not follow US EPA's change and stayed with its 50-µg/L standard.

Stay informed

Email Subscription Topic

Subscribe to the Drinking Water Program email topic to receive notifications and the latest updates.