EPA legal limit
No federal limit
Maximum Contaminant Level
EWG health guideline
0.02 ppb
Science-based, stricter target
IARC classification
Group 1 (inhaled) / Group 2A (ingested)
Cancer research classification
Health effects
Hexavalent chromium is classified by IARC as a Group 1 carcinogen via inhalation — well-established from occupational exposure in chrome plating and manufacturing. Via ingestion in drinking water, the carcinogenic evidence is classified as probable. A 2008 National Toxicology Program study found gastrointestinal tumours in animals at levels above 170 ppb. California's public health goal (0.02 ppb) is derived from a one-in-one-million cancer risk model. The gap between the federal total chromium MCL (100 ppb) and California's chromium-6 specific MCL (10 ppb) and the EWG guideline (0.02 ppb) reflects the difference between regulatory feasibility and health-protective thresholds.
Where it comes from
Two routes: industrial contamination (electroplating, leather tanning, metal finishing, improper disposal of chromate compounds — the source in the Hinkley case) and natural geological sources (chromium-bearing rock formations, particularly ultramafic geology in California, the Pacific Northwest, and parts of the Southwest). EWG analysis has found chromium-6 detections in water systems across nearly all US states.
How it's regulated
Federal: EPA MCL for total chromium 100 ppb — does not distinguish chromium-6 from chromium-3 (the safe, essential trace mineral form). No federal chromium-6 specific MCL as of May 2026. California: chromium-6 MCL 10 ppb, effective July 2024 — the first US jurisdiction with an enforceable chromium-6 specific standard. EWG health guideline: 0.02 ppb. For California utilities, WaterHealthCheck displays chromium-6 against the state-specific MCL separately from the federal total chromium standard.
How to filter chromium-6
Not all filters address chromium-6. Look for independently certified filters—NSF International certification means the removal claim has been independently verified.
Frequently asked questions
Is chromium-6 regulated in US drinking water?
The EPA regulates total chromium at 100 ppb — but this covers all chromium forms, not specifically hexavalent chromium (Cr-VI). There is no federal MCL specifically for chromium-6 as of May 2026. California adopted the first US chromium-6 specific MCL (10 ppb) in July 2024. A federal chromium-6 standard has been under consideration for years without finalisation.
What is the difference between chromium-3 and chromium-6?
Trivalent chromium (Cr-III) is an essential trace mineral that supports glucose metabolism — not considered a health concern at typical drinking water concentrations. Hexavalent chromium (Cr-VI) is a toxic, oxidised form associated with cancer risk. The EPA's total chromium MCL does not distinguish between them — water meeting the federal limit could contain significant chromium-6.
What water filter removes chromium-6?
Reverse osmosis (NSF 58 certified) removes 85–99% of chromium-6 and is the most reliable household option. NSF 53-certified activated carbon block filters can also reduce chromium-6 — verify that chromium is specifically listed in the product's NSF performance data sheet, as not all NSF 53 filters are tested for it. Standard pitcher filters are not certified for chromium-6 removal.
How does chromium-6 get into tap water?
Two main routes: industrial contamination (electroplating, leather tanning, metal finishing, and improper disposal of chromate compounds — the source in the Hinkley, California case made famous by Erin Brockovich) and natural geological sources (chromium-bearing rock formations, particularly in California, the Pacific Northwest, and parts of the Southwest).
Does my water have chromium-6?
EWG analysis has found chromium-6 detections in water systems across nearly all US states, though most detections are at low levels. Occurrence is highest near industrial sites and in areas with chromium-bearing geology. Enter your ZIP code to see your utility's chromium monitoring data from EPA SDWIS. For California utilities, state-specific chromium-6 data is also displayed.
Is chromium-6 in your water?
Enter your ZIP code to see the measured level in your specific utility.