⚗ Hexavalent chromium

Chromium-6 Contamination Map

Chromium-6 (hexavalent chromium) is a carcinogen that occurs both naturally in some rock formations and from industrial contamination. Unlike lead and PFAS, there is no federal maximum contaminant level — only California has set an enforceable MCL of 10 µg/L. See how every state compares.

3,927

Cities with chromium-6 detected

15,616

Cities with testing data

None

Federal maximum contaminant level

10 µg/L

California MCL — the only state limit

0%20%40%60%80%+ No data

Percentage of cities with chromium-6 detected in drinking water

⚠

There is no federal limit for chromium-6. The EPA regulates total chromium at 100 µg/L but has no separate standard for the carcinogenic hexavalent form. A 2010 EPA assessment found chromium-6 "likely to be carcinogenic to humans" by ingestion — but a final drinking water rule has not been finalized at the federal level.

Chromium-6 contamination: key numbers

0.02 µg/L

California's public health goal for chromium-6 — the level associated with a 1-in-a-million lifetime cancer risk

10 µg/L

California's enforceable MCL for chromium-6 — the only state with a specific hexavalent chromium drinking water limit

100 µg/L

EPA's federal MCL for total chromium (hexavalent + trivalent combined) — set in 1991, before chromium-6 was classified as a likely carcinogen

2013–2015

UCMR 3 monitoring period — the first time EPA required nationwide chromium-6 testing in public water systems

Erin Brockovich

The 2000 film that brought chromium-6 contamination from PG&E's Hinkley, CA compressor station to national attention

Natural + Industrial

Chromium-6 sources: naturally occurring in some rocks and soils, and from industrial discharge, electroplating, and chrome paint manufacturing

States ranked by chromium-6 detection rate

Percentage of cities where chromium-6 was detected at any level. There is no federal MCL — detections do not constitute a violation. Data from EPA UCMR 3 (2013–2015). California's 10 µg/L MCL is shown for reference.

#	State	Cities with detections	Cities tested	Detection rate	Max level (µg/L)
1	AP	21	21	100%	3
2	Connecticut	113	158	72%	1.2
3	Rhode Island	25	35	71%	0.26
4	New Jersey	290	435	67%	3.8
5	Massachusetts	147	280	53%	20
6	California	330	694	48%	47
7	Florida	165	388	43%	2.6
8	Kentucky	98	246	40%	1.5
9	Tennessee	109	299	36%	1.5
10	South Carolina	64	196	33%	0.64
11	Washington	91	294	31%	9.9
12	Hawaii	20	66	30%	9.7
13	Alabama	102	353	29%	3.2
14	Maine	49	168	29%	2.6
15	Virginia	66	230	29%	1.2
16	Delaware	12	43	28%	4.7
17	Nevada	17	66	26%	12
18	New York	226	855	26%	7.3
19	North Carolina	110	417	26%	11
20	Ohio	132	511	26%	3.2

Understanding chromium-6 in drinking water

What is chromium-6?

Chromium-6, or hexavalent chromium (Cr(VI)), is one of two common forms of chromium. While trivalent chromium (Cr(III)) is an essential trace nutrient, hexavalent chromium is toxic and classified by EPA as "likely to be carcinogenic to humans" when ingested. It occurs naturally when chromium-bearing minerals oxidize in certain rock formations, and from industrial sources including electroplating operations, leather tanning, chrome paint, and wood preservatives.

Health effects

A 2010 National Toxicology Program study found chromium-6 in drinking water caused cancer in laboratory animals. Long-term exposure is associated with stomach cancer, liver and kidney damage, and reproductive harm. California's public health goal of 0.02 µg/L was set at the level associated with a 1-in-a-million lifetime cancer risk — the state's enforceable MCL of 10 µg/L represents a policy compromise between health protection and treatment feasibility.

Why there is no federal MCL

The EPA's current federal standard for total chromium (100 µg/L, set in 1991) predates the agency's carcinogen classification of chromium-6. In 2014, EPA proposed to develop a separate chromium-6 MCL but has not finalized one. Environmental groups and California have sued over the delay. In the absence of a federal standard, utilities are only required to test and report chromium-6 under UCMR 3 — but are not required to reduce it below 100 µg/L total chromium.

The Hinkley, CA case

Pacific Gas & Electric's use of chromium-6 as a rust inhibitor in cooling tower water at its Hinkley, CA compressor station contaminated the local groundwater for decades. Legal action by attorney Erin Brockovich resulted in a 1996 settlement of $333 million — the largest settlement ever paid in a US direct-action lawsuit. The case, depicted in the 2000 film "Dark Waters," put chromium-6 contamination on the public radar and eventually drove California's 2014 MCL.

Reducing chromium-6 exposure

Reverse osmosis systems remove 85–95% of chromium-6 and are certified under NSF/ANSI 58. Strong base anion (SBA) ion exchange resins achieve 95–99% removal and are used in municipal treatment upgrades. Coagulation/filtration at the utility level can reduce chromium-6 by 70–90%. Standard activated carbon filters are not effective against chromium-6. Check that any filter you purchase has NSF certification specifically listing chromium-6 reduction.

About this data

This map uses chromium-6 data from EPA's UCMR 3 monitoring program (2013–2015) — the first nationwide testing requirement for hexavalent chromium in public water. The program covered systems serving 10,000+ people plus a statistical sample of smaller systems. Detection rates on this map reflect any measured chromium-6, not exceedance of a limit (since no federal limit exists). Cities are colored by detection rate, not concentration.

Frequently asked questions

Is chromium-6 detection in my water dangerous?

Detection at low levels may not pose an immediate health risk — the degree of risk depends on the concentration. California's public health goal of 0.02 µg/L represents a 1-in-a-million cancer risk level; its enforceable MCL of 10 µg/L reflects a policy balance. Without a federal MCL, there is no legally required action level for most utilities. If your water system detected chromium-6, check the specific concentration in your Consumer Confidence Report and compare it to California's 10 µg/L limit as a reference point.

Does my city have to tell me if chromium-6 is detected?

Under UCMR 3, utilities were required to test and report results to EPA — but because there is no federal MCL for chromium-6 specifically, detections don't trigger public notification requirements on their own. Your utility must report total chromium in its annual Consumer Confidence Report. If you want chromium-6 specifically, you can request results directly from your water system or look up UCMR 3 data in EPA's public database.

Will EPA ever set a federal chromium-6 limit?

EPA has been working toward a chromium-6 MCL since 2011 when it began a risk assessment, and proposed to develop one in 2014. As of 2026, a final rule has not been issued. Environmental groups continue to push for action, and some states are considering their own limits following California's lead. The lack of a federal standard means chromium-6 remains one of the most significant unregulated carcinogens in US drinking water.

What filters remove chromium-6?

Reverse osmosis (NSF/ANSI 58) removes 85–95% of chromium-6 and is the most accessible point-of-use option. Strong base anion ion exchange systems achieve 95–99% removal. Standard pitcher filters and refrigerator filters are not effective. When buying a filter, look for NSF certification that specifically lists chromium-6 (hexavalent chromium) reduction — not just total chromium.

Check chromium-6 levels in your city

Search for your city to see whether chromium-6 was detected, concentration data from UCMR 3 testing, and filter recommendations for your water supply.

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