Chromium
Cr·Affects kidneys, liver, lungs
A heavy metal that exists in two main forms: trivalent chromium (a trace nutrient) and hexavalent chromium-6 (a known carcinogen). The hexavalent form contaminates municipal supplies in dozens of US states.
Cr
EPA limit
0.1 mg/L (100 ppb), total chromium
Most at risk
Residents downstream of metal plating, leather tanning, and cooling tower facilities
Found in
City water · Well water · Industrial areas
AquaOx filters
YesKDF-55 + activated carbon (paired with RO for hexavalent chromium)
What it does to you
Health effects
The toxicity of chromium depends on its valence state. Trivalent chromium (Cr-3) is an essential trace nutrient involved in glucose metabolism and is poorly absorbed through the gut. Hexavalent chromium (Cr-6) is the dangerous form: classified by the EPA and IARC as a known human carcinogen when inhaled and a probable carcinogen when ingested.
Chronic Cr-6 exposure through drinking water damages the liver and kidneys, where the metal accumulates after being absorbed. The lungs are also a target, particularly from inhalation of mist during showering, and from occupational dust exposure in plating shops.
The EPA's 100 ppb federal MCL covers total chromium (Cr-3 plus Cr-6 combined). California has set a much stricter state-level Cr-6 limit at 10 ppb, reflecting the consensus that hexavalent chromium is toxic at levels far below the federal standard.
Where it comes from
How it gets into your water
Hexavalent chromium reaches drinking water primarily through industrial discharge: chrome plating, stainless steel and leather tanning, textile dye manufacturing, pulp and paper mills, and the corrosion inhibitors used in industrial cooling towers. Improperly managed waste sites and unlined landfills have created Cr-6 plumes in groundwater across many states.
Natural geological sources contribute in some regions, with Cr-6 forming when chromium-bearing rock weathers in oxygen-rich aquifers. This is the case in parts of California, Arizona, and the Mojave region.
Both forms can also enter tap water from corroding pipes and fittings that contain chromium alloys, although industrial discharge remains the dominant pathway in contaminated zones.
Chrome plating and metal finishing
Major Cr-6 discharge source
Leather tanning and dye manufacturing
Historic and active sites
Cooling tower corrosion inhibitors
Legacy contamination plumes
Natural geology
Weathering of chromium-bearing bedrock
Find out for yourself
Is it in your water?
Federal Consumer Confidence Reports list total chromium, but they don't always break out the hexavalent fraction. The Environmental Working Group's national Tap Water Database lets you look up Cr-6 levels by zip code, drawn from utility testing data, and shows that detectable Cr-6 is widespread.
Private well users in industrial corridors or near former plating, tanning, or aerospace sites should test specifically for hexavalent chromium (most standard panels report only total chromium). Wells in geological hot spots (California's Central Valley, the Mojave, parts of the Southwest) should also be tested.
The fix
How AquaOx filters it
AquaOx's KDF-55 copper-zinc media reduces hexavalent chromium to the much less toxic trivalent form through redox chemistry, then captures it in the filter bed. The activated carbon stage provides secondary adsorption of residual chromium species.
For well sources or municipalities with documented Cr-6 above health-based screening levels, AquaOx recommends pairing the whole-house system with a point-of-use reverse osmosis unit at the kitchen sink. RO membranes reject both Cr-3 and Cr-6 to very low levels, giving you a dedicated barrier for the water you actually drink.