Chromium-6 (Hexavalent Chromium)
The Erin Brockovich chemical. A known carcinogen with no federal-specific limit yet.
The science, plainly.
Chromium-6 is a heavy metal used in industrial processes like chrome plating, leather tanning, and stainless steel manufacturing. It can also occur naturally. Famously the contaminant at the center of Hinkley, California (and the Erin Brockovich case), it is a known human carcinogen when inhaled and is classified as a likely carcinogen when ingested.
The pathways into the tap.
- Industrial discharge (chrome plating, leather, stainless steel)
- Cooling tower additives
- Naturally in some bedrock
- Coal combustion ash
What the evidence shows.
Strong evidence of carcinogenicity via inhalation. For ingestion, animal studies and some epidemiology suggest stomach and intestinal cancer risk. Liver, kidney, and reproductive effects are also documented at higher doses.
Cancer
Established carcinogen via inhalation; classified as 'likely to be carcinogenic to humans by ingestion' by EPA.
Liver / kidney
Damage observed in animal studies at elevated doses.
Reproductive
Some animal data on reproductive and developmental harm.
What the law allows vs. what's actually safe.
EWG guideline of 0.02 ppb is based on 2008 NIH National Toxicology Program animal data; 5,000× stricter than the total-chromium MCL.
Note: EPA proposed a chromium-6-specific MCL in 2025, but no final rule existed at the time of this writing. California is the only state with an enforceable Cr-6 standard (10 ppb).
Where exposure is highest.
Detected in the tap water of more than 200 million Americans according to EWG sampling. Highest near industrial corridors, especially Southern California, the Carolinas, and parts of the Rust Belt.
Filtration that actually works.
- Reverse osmosis
- Ion exchange (specifically for Cr-6)
- Distillation
We don't recommend brands. The certification on the box matters more than the brand printed on it. Look for the actual NSF/ANSI standard number specific to the contaminant you're removing.
Sources
- National Primary Drinking Water Regulations — U.S. Environmental Protection Agency
- Tap Water Database — Environmental Working Group