Chromium-6
Cr⁶⁺·Affects liver, kidneys, lungs
The toxic, carcinogenic form of chromium made famous by Erin Brockovich and the Hinkley, California groundwater case. EPA has no separate federal limit yet; California regulates it at 10 µg/L.
Cr⁶⁺
EPA limit
0.010 mg/L (California; no separate federal MCL)
Most at risk
Residents near industrial sites, communities on contaminated aquifers, pregnant women, children
Found in
City water · Well water · Industrial areas
AquaOx filters
YesKDF-55 + activated carbon (RO for complete removal)
What it does to you
Health effects
Hexavalent chromium is a confirmed Group 1 human carcinogen under the International Agency for Research on Cancer. The strongest evidence comes from inhalation exposure in occupational settings, but oral exposure through drinking water is associated with stomach and gastrointestinal tumors in long-term animal studies and elevated cancer rates in exposed populations.
The kidneys and liver are the primary chronic-exposure target organs, with measurable damage at sustained low doses. Chromium-6 is also a potent skin sensitizer and can trigger allergic contact dermatitis in shower water exposures.
This is the contaminant at the center of the Hinkley, California case dramatized in the film Erin Brockovich. Pacific Gas and Electric discharged hexavalent chromium into unlined ponds for decades, contaminating the town's groundwater and producing the cancer cluster that drove the 1996 settlement.
Where it comes from
How it gets into your water
Chromium-6 enters water from industrial discharges, particularly from metal plating, leather tanning, stainless-steel production, textile dye manufacturing, and chemical wood preservatives. It also leaches from coal-ash ponds and cooling-tower waste.
Some chromium-6 occurs naturally in groundwater from erosion of chromium-bearing rock, but the high-concentration contamination events are almost always industrial. Aging water-treatment infrastructure can also convert the less toxic chromium-3 into chromium-6 during chlorination.
Metal plating and finishing
Chrome plating shops and electroplaters
Coal-ash and power-plant waste
Leaches from unlined disposal ponds
Leather tanning and textile dyes
Process discharges into wastewater
Natural geological deposits
Chromium-bearing bedrock in parts of the West
Find out for yourself
Is it in your water?
Most utilities still report only total chromium on their Consumer Confidence Reports, which lumps together the relatively benign chromium-3 and the toxic chromium-6. The Environmental Working Group's 2016 nationwide tap-water analysis detected chromium-6 in the systems of more than 200 million Americans, often well above California's 10 µg/L limit even though the levels were legal federally.
If you live near a former industrial site, a coal-ash facility, or a known chromium-6 plume, request a specific hexavalent chromium test from a certified lab. Well owners in California, Nevada, and parts of the Southwest have higher background risk from natural geology.
EPA proposed a federal MCL for hexavalent chromium in 2024 but has not yet finalized it. California remains the regulatory frontier with its 0.010 mg/L standard.
The fix
How AquaOx filters it
The KDF-55 stage in every AquaOx system uses copper-zinc redox chemistry to reduce a portion of hexavalent chromium to the less toxic trivalent form, which then precipitates out of solution. The activated carbon stages add adsorption capacity for residual chromium compounds.
Because hexavalent chromium is so carcinogenic and so difficult to fully filter with a single technology, AquaOx recommends pairing the whole-house system with point-of-use reverse osmosis at the kitchen sink whenever chromium-6 is a documented concern in your area. RO membranes reject chromium-6 to below California's 10 µg/L standard and give you a dedicated barrier for drinking and cooking water.