California — Maximum Contaminant Level for Hexavalent Chromium in Drinking Water

California’s drinking-water Maximum Contaminant Level (MCL) for hexavalent chromium (Cr-VI) is 0.010 mg/L, equal to 10 µg/L or 10 ppb. The State Water Resources Control Board adopted the regulation on April 17, 2024; the Office of Administrative Law approved it on July 24, 2024; and it took effect on October 1, 2024 (SWRCB Cr-VI MCL). The MCL is the first enforceable concentration limit in California to address hexavalent chromium specifically rather than through the broader total-chromium MCL of 50 µg/L (SWRCB Cr-VI MCL).

This is a drinking-water standard, not a food limit. It governs the concentration of hexavalent chromium permitted in water delivered by public water systems in California. There is no California or US regulatory maximum level for hexavalent chromium in a food matrix; this MCL is cited on the wiki as the closest ingestion-route Cr-VI regulatory benchmark, derived from drinking-water toxicology rather than from food-occurrence data. See Chromium, Hexavalent for the species synthesis and the food-occurrence evidence base.

Scope

The MCL applies to community water systems and nontransient-noncommunity water systems in California (SWRCB Cr-VI MCL). It is an enforceable concentration limit on water as delivered to consumers. It does not set a per-day exposure value, a product-labeling threshold, or a food contaminant level, and it should not be compared directly to a food-occurrence concentration.

Exact limit and units

The OEHHA Public Health Goal (PHG) for hexavalent chromium is 0.02 µg/L, set in 2011 (SWRCB Cr-VI MCL). The PHG is the concentration posing no significant lifetime health risk; the enforceable MCL of 10 µg/L is set above it because California must weigh detection, treatment, and cost-feasibility when establishing an MCL. The State Water Board’s documentation estimates a residual lifetime cancer risk on the order of 1 in 2,000 for a person consuming two liters per day for 70 years at the MCL (SWRCB Cr-VI MCL).

How tested

Hexavalent chromium in drinking water is measured by ion chromatography with post-column reaction, the method family that preserves the Cr-VI species rather than reducing it to trivalent chromium during digestion (US EPA Method 218.6 and the later Method 218.7). Total-digestion methods used in food-occurrence surveys report total chromium and cannot substitute for a Cr-VI measurement. See the testing discussion on Chromium, Hexavalent for the speciation constraint in detail.

Enforcement posture

Compliance monitoring is phased. Community and nontransient-noncommunity systems were required to complete initial monitoring on or before April 1, 2025, with full compliance staggered by system size: October 1, 2026 for systems with 10,000 or more service connections, October 1, 2027 for systems with 1,000 to 9,999 connections, and October 1, 2028 for systems with fewer than 1,000 connections (SWRCB Cr-VI MCL).

History of changes

California first adopted a hexavalent-chromium MCL of 10 µg/L (rule DPH-11-005) that took effect in 2014. In 2017 the Superior Court of Sacramento County invalidated that regulation, holding that the State had not adequately documented why the MCL was economically feasible as required by California law (SWRCB Cr-VI MCL). The 2014 MCL was withdrawn, leaving hexavalent chromium regulated only through the total-chromium MCL of 50 µg/L until the present regulation re-established a Cr-VI-specific MCL at the same numeric value of 10 µg/L, effective October 1, 2024.

How it compares

The federal Safe Drinking Water Act has no hexavalent-chromium-specific MCL; the US EPA national primary drinking-water regulation sets a total-chromium MCL of 100 µg/L, and California’s total-chromium MCL is 50 µg/L. California’s Cr-VI MCL of 10 µg/L is therefore both species-specific and substantially tighter than any federal chromium standard. For the federal arsenic analogue of a 10 ppb drinking-water MCL, see EPA — Maximum Contaminant Level for Arsenic in Drinking Water. The separate California Proposition 65 listing of hexavalent chromium, which governs product warnings rather than water concentration, is covered at California Proposition 65 — Hexavalent Chromium Listing and Safe-Harbor Levels.

Sources

• SWRCB Cr-VI MCL — California State Water Resources Control Board, Division of Drinking Water. Hexavalent Chromium MCL Regulation (SWRCB-DDW-21-003), effective October 1, 2024.

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