Chromium-6 (Hexavalent Chromium) in Drinking Water

Data source: U.S. EPA, California OEHHA, National Toxicology Program

What Is Chromium-6?

Chromium-6 (hexavalent chromium, Cr(VI)) is one of two primary forms of chromium found in drinking water. Unlike trivalent chromium (Cr(III)), which is an essential trace nutrient, hexavalent chromium is a recognized carcinogen. It became widely known to the public through the Hinkley, California groundwater contamination case documented by Erin Brockovich in the 1990s — but contamination extends well beyond that single case to thousands of communities nationwide.

Chromium-6 is colorless in water and cannot be detected by taste or smell at typical concentrations.

Health Effects

Chromium-6 is classified as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC) for inhalation exposure. For ingestion via drinking water, the evidence includes:

• Cancer risk — stomach and small intestine cancers in animal studies at high concentrations; epidemiological studies suggest increased risk in heavily contaminated areas
• Reproductive effects — animal studies indicate developmental and reproductive toxicity at elevated doses
• GI effects — high-dose ingestion causes stomach irritation and ulceration

The California Office of Environmental Health Hazard Assessment (OEHHA) calculated a Public Health Goal (PHG) of 0.02 ppb — among the most stringent in the country — based on cancer risk assessment. California set a Maximum Contaminant Level (MCL) of 10 ppb in 2014 but it was overturned in 2017 pending cost analysis; regulatory action at the state level continues.

At the federal level, no MCL exists specifically for chromium-6; only a total chromium standard of 0.1 mg/L (100 ppb) is in effect.

How Chromium-6 Gets Into Water

• Industrial discharge — electroplating, leather tanning, textile manufacturing, and steel production generate hexavalent chromium waste; historic disposal practices contaminated groundwater near industrial sites across the U.S.
• Natural erosion — chromium is naturally present in rock and soil; oxidizing conditions convert some trivalent chromium to hexavalent form, particularly in the western U.S.
• Coal ash — combustion residuals from coal-fired power plants contain chromium and other heavy metals; improper disposal contaminates nearby groundwater
• Military sites — chrome-containing compounds were used in maintenance and manufacturing at military installations

A 2016 Environmental Working Group (EWG) analysis found chromium-6 in the tap water of all 50 states at concentrations above California's PHG, affecting an estimated 218 million Americans.

EPA Standards

The EPA's MCLG for total chromium is 0.1 mg/L, and the agency has been evaluating a separate standard for chromium-6 for over a decade without finalizing one. The regulatory gap means utilities are not specifically required to monitor or reduce chromium-6 below 100 ppb, even though health concerns exist at much lower concentrations.

How to Remove Chromium-6 From Drinking Water

Standard pitcher-style carbon filters are not effective for chromium-6 removal. Effective methods include:

• Reverse osmosis (RO) — removes 85–95% of total chromium including Cr(VI); NSF 58 certified; most practical point-of-use option
• Strong-base anion exchange resin — highly effective for chromate (the dominant form of Cr(VI) in water); used in point-of-use and point-of-entry systems
• Reduction media — ferrous iron-based media reduces Cr(VI) to Cr(III), which then precipitates; used in whole-house systems
• Coagulation-filtration — used at the utility scale; not practical for home use

For point-of-use systems, RO certified under NSF 58 with specific reduction claims for total chromium provides the most accessible protection.

Chromium-6 in U.S. Water Systems: What the Data Shows

ZipCheckup aggregates CCR data and EPA enforcement records to track chromium contamination across the country:

• 4 water systems serving 126 ZIP codes reported hexavalent chromium detections in their most recent Consumer Confidence Reports
• 534 EPA enforcement actions for chromium (total and hexavalent) have been recorded across 91 ZIP codes
• In total, chromium-related data affects 217 ZIP codes in our database

Because there is no federal MCL specifically for chromium-6, enforcement actions are recorded under total chromium (100 ppb). Many systems with detectable chromium-6 at levels far above California's 0.02 ppb health goal show no federal violations.

Is Chromium-6 a Problem in Your Area?

Given the absence of a federal chromium-6 MCL, communities may have elevated levels that go unregulated. The highest-risk areas historically include California's San Joaquin Valley, regions near former industrial sites, coal-burning power plant corridors, and areas with naturally chromium-bearing geology.

ZipCheckup displays total chromium violation data from EPA SDWIS. Because no federal chromium-6-specific MCL exists, violations are recorded under total chromium only.