Chromium-6 in US Tap Water: Where It's Found and How High
Health disclaimer: This page provides general information about chromium-6 in public drinking water. It is not medical advice. If you have concerns about chromium-6 exposure, contact your water utility for their most recent testing data and consult your doctor regarding any health concerns.
There’s no federal limit specifically for chromium-6 in drinking water. There’s a limit for total chromium at 100 ppb, but total chromium combines the harmless form with the carcinogen. California finally set a specific chromium-6 limit in 2024. The EPA still hasn’t.
That regulatory gap is why chromium-6 coverage matters. Utilities can have detectable chromium-6 in their water, stay well within the 100 ppb total chromium limit, and have no obligation to reduce it further under current federal rules.
Where Chromium-6 Is Found at High Levels
EWG’s analysis of utility testing data, published in 2016 and updated since, found chromium-6 in tap water serving approximately 250 million Americans across 48 states. Most of those detected levels are low. But the geographic pattern of higher concentrations is consistent.
The highest levels have turned up in parts of California, Texas, Oklahoma, Arizona, and North Carolina. Some utilities in those states have reported chromium-6 above 10 ppb, which is now California’s legal limit. That same level would be legal under current federal rules everywhere else.
Two different source types drive contamination. Industrial discharge accounts for high chromium-6 near metal plating facilities, leather tanneries, and former manufacturing sites. Chromium-6 was also widely used as a corrosion inhibitor in cooling towers, which is the source that put Hinkley, California on the map. Pacific Gas and Electric’s use of chromium-6 in cooling tower water at their Hinkley compressor station contaminated local groundwater from the 1950s through the 1960s. That case, documented in the 2000 film “Erin Brockovich,” established chromium-6 as a nationally recognized water quality concern.
But natural geology also matters. The western US has chromium-rich rock formations, and chromium-6 leaches from those formations into groundwater without any industrial activity involved. Parts of California, Nevada, and Arizona have naturally high chromium-6 in groundwater that pre-dates industrial activity in those areas.
The Regulation Gap
The EPA’s current MCL for total chromium is 100 ppb. That limit was set in 1991, before the health science on chromium-6 specifically was well developed.
The problem with regulating total chromium is that it lumps chromium-3 (a nutrient) with chromium-6 (a carcinogen). A utility could have 90 ppb of chromium-3 and 10 ppb of chromium-6 and technically comply with the total chromium limit. Under current federal rules, that’s fine.
California’s approach is different. In April 2024, California adopted an MCL of 10 ppb specifically for chromium-6. It’s the first state chromium-6 standard in the country. Utilities in California must now test for chromium-6 separately from total chromium and meet the 10 ppb limit.
The EPA has been moving toward a federal chromium-6 rule for years. A proposed rule has been through multiple rounds of comment and review. As of early 2026, no final federal MCL for chromium-6 exists. The EPA’s 2021 Regulatory Agenda listed chromium-6 as a priority, but finalization timelines have shifted repeatedly.
Health Effects
California’s Office of Environmental Health Hazard Assessment (OEHHA) classifies chromium-6 as a known human carcinogen when ingested. That classification is based on epidemiologic data from Hinkley and on animal studies showing intestinal tumors at high exposure levels.
The Hinkley data showed higher rates of specific cancers in the affected population compared to surrounding communities. Researchers have been cautious about quantifying exact risk at low doses from those findings, because the exposure levels in Hinkley were high and the exposed population was relatively small.
The EPA’s own cancer assessment concluded that chromium-6 is likely carcinogenic to humans via ingestion. The MCLG question is central here. The MCLG is the health-based goal, set without regard to cost or technical achievability. For known carcinogens, the MCLG is typically zero. If the EPA finalizes a chromium-6 rule with an MCLG of zero, that would mean any detected level above the regulatory limit represents an acknowledged risk trade-off, similar to how the EPA handles arsenic.
How to Check Your Level
Your utility’s Consumer Confidence Report (CCR) is the starting point. Utilities that serve 25 or more connections are required to publish CCRs annually. The report lists contaminants detected during the reporting year, along with the levels found and the applicable MCLs. Look for total chromium. If your utility has started reporting chromium-6 separately due to California requirements or voluntary testing, that will appear as a distinct row.
EWG’s tap water database at ewg.org/tapwater lets you enter your zip code and see what your utility has reported for chromium. EWG presents the data alongside their own health benchmarks, which are more stringent than EPA MCLs. Don’t confuse EWG’s health benchmarks with legal limits. They’re different numbers with different purposes.
If your utility reports total chromium near or above 10 ppb, or if you’re in an area with a history of industrial contamination, you can also get your tap water tested by a certified lab for chromium-6 specifically. See the best mail-in water tests page for lab options, and the how to read your water quality report guide for help making sense of utility data.
What Removes Chromium-6
Reverse osmosis (RO) is the most accessible treatment for household chromium-6 removal. RO systems certified to NSF/ANSI 58 have been tested for heavy metal reduction including chromium. An under-sink RO handles drinking and cooking water at the tap, which covers the primary ingestion pathway.
Activated carbon alone doesn’t reliably address chromium-6. Standard pitcher filters and faucet-mounted carbon units aren’t effective here. Don’t count on them.
For treatment details and product options, see how to remove chromium-6 from water.
For background on chromium-6 health effects, regulation, and the gap between California’s 10 ppb limit and federal law, see the chromium-6 contaminant overview.
Sources
- EWG, “Chromium-6 Is Widespread in US Tap Water”: ewg.org/research/chromium-6-widespread-in-us-tap-water
- California State Water Resources Control Board, “Hexavalent Chromium (Chromium-6) Maximum Contaminant Level”: waterboards.ca.gov
- EPA, “National Primary Drinking Water Regulations, Chromium”: epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations
- California OEHHA, “Chromium Hexavalent (Chromium-6)”: oehha.ca.gov
Health disclaimer: This page provides general information about chromium-6 in tap water. It is not medical advice. For your current utility data, check your Consumer Confidence Report or contact your water provider. If you have health concerns related to chromium-6 exposure, consult your doctor.