An element often present in ground water in a soluble form (such as ferrous bicarbonate) in quantities usually ranging from 0.5 to 10 ppm. Iron may exist in surface waters due to natural causes or pollution. Iron in solution is susceptible to oxidation, precipitating as a reddish-brown floc when contacted by air (causing staining and discoloration). Iron can be removed by aeration or chlorination followed by filtration. Iron in solution can be removed by ion exchange. Oxidizing filters such as manganese treated zeolite are used for removing large amounts of iron from household water supplies.