What is chromium-6 and why is it dangerous?

Chromium-6 (hexavalent chromium, Cr(VI)) is the toxic form of chromium — the compound at the center of the Erin Brockovich case in Hinkley, California. It is a probable human carcinogen based on studies showing increased lung cancer in workers exposed via inhalation and stomach cancer in animal studies with oral exposure. Unlike chromium-3 (trivalent chromium, a dietary nutrient), chromium-6 has no nutritional value and causes DNA damage. The EPA's current total chromium MCL of 100 ppb does not distinguish between the toxic and non-toxic forms — a major regulatory gap.

Is chromium-6 in my tap water?

Probably yes, at some level. The Environmental Working Group analyzed EPA monitoring data and found chromium-6 in the tap water of all 50 states — at detectable levels in water serving 218 million Americans. The question is the concentration. The EWG health guideline is 0.02 ppb (parts per billion) — their estimate of a one-in-one-million cancer risk level. Most U.S. water contains chromium-6 levels above 0.02 ppb. California set a drinking water standard of 10 ppb specifically for chromium-6 in 2023.

What filter removes chromium-6?

Reverse osmosis certified to NSF/ANSI 58 removes 85–95% of chromium-6. Strong base anion exchange resins remove nearly 100% but are not typically used in consumer applications. Certain activated carbon block filters are NSF/ANSI 53-certified for total chromium reduction, but certification data for chromium-6 specifically is less common. The Clearly Filtered pitcher is NSF certified for chromium-6 reduction. Always verify the specific certification for Cr(VI) — not just total chromium — when purchasing.

How to Remove Chromium-6 (Hexavalent Chromium) from Drinking Water

Chromium-6: The Erin Brockovich Contaminant in Most U.S. Water

Most people know chromium-6 from the Erin Brockovich story — Pacific Gas & Electric contaminated the groundwater in Hinkley, California with hexavalent chromium from industrial operations, and the resulting legal case became a landmark environmental lawsuit. What most people don't know is that chromium-6 is not just a California problem. It's found in tap water serving the majority of Americans.

The EWG's analysis of EPA monitoring data found chromium-6 at detectable levels in drinking water serving 218 million Americans across all 50 states. Industrial use, natural geological sources (particularly in the western states and certain eastern rock formations), and release from chromite ore processing are all sources. At high concentrations (thousands of ppb), chromium-6 is unambiguously toxic. At the lower levels found in most U.S. water supplies (0.1–10 ppb), the carcinogenic risk is debated but present.

The Regulatory Gap

The EPA's current MCL of 100 ppb covers total chromium — it doesn't distinguish between chromium-3 (benign, a dietary nutrient) and chromium-6 (carcinogenic). California set a specific Cr(VI) standard of 10 ppb in 2023. The federal EPA has not updated its standard to address this. Compliance with the 100 ppb MCL does not guarantee your water is chromium-6-safe at health-protective levels.

What Removes Chromium-6

The filtration landscape for chromium-6 is more limited than for lead or PFAS. Here's what works:

Reverse Osmosis — Best Option

NSF/ANSI 58-certified RO removes 85–95% of Cr(VI). The RO membrane physically excludes the chromate ion (CrO4²⁻). Any NSF 58-certified RO system will reduce chromium-6 substantially. Our tested recommendation: the Waterdrop G3P800 or iSpring RCC7.

NSF/ANSI 53-Certified Carbon Block

Select carbon block filters are NSF 53 certified for total chromium reduction. The Clearly Filtered Pitcher is one of the few pitchers with certification data specifically for chromium-6, claiming 99.8% reduction. Check the NSF Certified Products Database and look specifically for Cr(VI) reduction claims.

Testing for Chromium-6

Standard water tests report total chromium, not chromium-6 specifically. Our Tap Score review covers which panels include chromium speciation testing. For chromium-6 testing, you need a lab that offers speciated chromium analysis. Tap Score's Core City Water Test ($179) includes total chromium; to test specifically for Cr(VI), request their Advanced Metals test ($299) which includes chromium speciation. Your utility's CCR reports total chromium — if that number is zero, Cr(VI) is also zero. If you see detectable total chromium, speciation testing will tell you how much is the toxic form.