Disclaimer: This page provides general information about chromium-6 in drinking water. It is not medical advice. If you have health concerns related to water quality, consult a licensed healthcare provider.
The Erin Brockovich case made chromium-6 famous. In the 1990s, Pacific Gas & Electric contaminated groundwater in Hinkley, California with chromium-6 from industrial cooling tower operations. A 1996 legal settlement paid $333 million to affected residents. It was the largest settlement in a direct-action lawsuit in US history at the time.
That was 30 years ago. The regulation still hasn’t caught up.
What Chromium-6 Is and Where It Comes From
Chromium-6, or hexavalent chromium, is one of several forms of chromium. The federal government regulates total chromium in drinking water, which means Cr-6 has no specific federal limit of its own.
Industrial sources include chrome plating facilities, metal finishing operations, aerospace manufacturing, and sites where chromate-based compounds were used in cooling systems. These operations can release Cr-6 into soil and groundwater, sometimes for decades before anyone detects it.
But not all Cr-6 comes from industrial contamination. Natural geological sources also release it. Chromium-bearing rock, serpentinite and ultramafic rock in particular, weathers over time, and that process moves Cr-6 into groundwater. Parts of California, Arizona, Nevada, and Texas have elevated natural background levels with no industrial source nearby.
That’s an important distinction. It means Cr-6 isn’t only a factory-town problem.
The Standards Gap
Here’s where it gets complicated.
The federal EPA does not have a specific MCL for chromium-6. The total chromium MCL is 100 parts per billion (ppb). If your utility reports chromium levels below 100 ppb, they’re in legal compliance, even if the water contains significant Cr-6.
California changed that in April 2024. The state adopted a chromium-6-specific MCL of 10 ppb, the first state in the US to do so. California’s Office of Environmental Health Hazard Assessment had previously recommended a public health goal of 0.02 ppb. That’s the level their scientists estimated would adequately protect health. The 10 ppb MCL was set not because 10 ppb is considered safe, but because it was deemed the lowest economically achievable limit for water systems statewide.
That 500-fold gap between the health goal and the regulatory limit is documented and not contested. It reflects the cost and technical difficulty of treating Cr-6 at scale across thousands of water systems.
At the federal level, EPA is required by legal settlement to issue a specific chromium-6 MCL by 2027. That rulemaking is underway.
Source: California Water Boards, Chromium-6
Health Effects: What the Research Actually Says
Chromium-6 is a confirmed carcinogen when inhaled in occupational settings. Workers in chrome plating and chromate manufacturing have elevated lung cancer rates. That link is well-established.
Drinking water is a different exposure pathway. Evidence from animal studies and occupational research suggests chromium-6 exposure above current limits may increase cancer risk. In animal studies, rats and mice drinking water with elevated Cr-6 developed stomach and intestinal tumors. Human drinking water data is still under active review.
The National Toxicology Program has classified Cr-6 as reasonably anticipated to be a human carcinogen. The IARC lists hexavalent chromium compounds as Group 1 carcinogens based on occupational inhalation data. The extrapolation to drinking water cancer risk is real, but ongoing research continues to refine those estimates.
The EPA’s pending rulemaking will incorporate the most current data before setting a federal limit.
How Widespread Is It
EWG’s Tap Water Database found chromium-6 in public water systems across all 50 states. Many of those detections fall below the total chromium federal MCL but above EWG’s health guideline of 0.02 ppb.
The highest concentrations tend to cluster in specific areas:
California has both geological and industrial sources. The Central Valley, the Mojave Desert region, and the San Gabriel Valley all have documented Cr-6 issues in groundwater. The state’s new 10 ppb MCL directly targets these systems.
Arizona and Nevada have significant geological background Cr-6 from ultramafic rock formations across the Colorado Plateau and Basin and Range regions.
Industrial areas nationwide face localized contamination near chrome plating shops, aerospace facilities, and legacy manufacturing sites. These aren’t limited to the West.
Source: EWG Tap Water Database
Municipal Water vs. Well Water
If you’re on a municipal system, your utility tests for total chromium. Check your Consumer Confidence Report (CCR). It’s mailed annually or available online. If you’re in California, your utility now must comply with the 10 ppb Cr-6 MCL and report results accordingly.
Well owners are in a different position. Private wells fall outside utility monitoring. A standard well test may not include chromium at all. If you’re in California, Arizona, Nevada, or near any industrial operation, you’ll want a certified lab test that specifically reports chromium-6 and total chromium separately. A total chromium result alone won’t tell you how much is in the more concerning Cr-6 form.
For a full picture of what to test for: Water Testing Guide
If you’re on a well, the well water testing guide covers how to find a certified lab and what to order.
Treatment Options That Actually Work
Two approaches have solid evidence for Cr-6 reduction at the point of use.
Reverse osmosis systems certified to NSF/ANSI 58 are the most practical option for most households. RO removes Cr-6 along with a broad range of other dissolved contaminants. An under-sink RO system treats the water at the kitchen tap where you drink and cook. See: Best Under-Sink RO Systems.
Strong base anion exchange resin is also effective. Chromium-6 exists as a negatively charged ion (chromate) in water, which makes it a good candidate for anion exchange. This approach is used in some whole-house and commercial systems.
What doesn’t work: standard activated carbon, pitcher filters without specific Cr-6 certification, and boiling. Boiling concentrates dissolved chromium just as it concentrates lead.
Who Should Test Now
If you’re in California on a municipal system, your utility is now subject to the 10 ppb MCL. Review your CCR for chromium results, or contact your utility directly.
If you’re on well water anywhere in California, Arizona, or Nevada, testing for chromium-6 specifically makes sense given regional geological sources.
If you live near a chrome plating shop, metal finishing facility, aerospace manufacturing site, or any legacy industrial operation, targeted chromium testing is worth doing regardless of state.
For everyone else, checking your CCR for total chromium gives you a baseline. If the number is anything above trace levels, consider a Cr-6-specific test from a certified lab.
Chromium-6 isn’t rare. It’s in water systems in every state. Federal regulation is coming, but the timeline runs to 2027. The practical answer right now is testing to know what you’re dealing with, and an NSF 58-certified RO system if levels warrant treatment.
Related: PFAS in Drinking Water is another contaminant that spent years without a specific federal limit before regulation caught up.
Disclaimer: WaterAnswer.com provides general information only. This page does not constitute medical advice. Consult a healthcare provider with health concerns related to water quality.