Cadmium, a soft, bluish-white metal impurity usually associated with zinc, enters the environment and becomes a water contaminant through a variety of industrial and agricultural operations and as a by product of fossil fuel use. General use has declined, and now about 80% of cadmium in the environment comes from nickel-cadmium batteries. Cadmium often enters water as the result of deterioration of galvanized plumbing, fertilizer contamination, and industrial waste in general.
Cadmium has an EPA Primary Standard contaminant level listing of 0.005 mg/l.
Cadmium can have many serious health effects. For a full discussion, visit the EPA's website.
Cadmium is easily removed from water by reverse osmosis (95 to 98%), by cation exchange (water softener), and by dialysis.
Sources: Enting Engineering Handbook. Wikipedia, EPA. A good source of Cadmium information, including the many adverse health issues associated with cadmium, is the EPA's website.