Chromium enters the water supply mainly as the a waste product of industry.

It exists as trivalent Chromium, which not only is not toxic but is considered an essential nutrient for humans, or a hexavalent Chromium, which is classed as a carcinogen by the EPA. The EPA's MCL for Cr -6 (hexavalent Chromium) is only 0.005 mg/l.

Fortunately, the occurrence or excessive Chromium is relatively infrequent. Removal from drinking water is accomplished by reverse osmosis (90% to 97%) or by distillation. For larger quantities, the best treatment for CR-6 is strong base anion exchange, which must be regenerate with caustic soda.