Iron in drinking water predominantly exists in two separate forms: soluble ferrous iron or insoluble ferric iron. Ferrous iron exists dissolved in water without altering the clarity or odor of the water, but can leave a metallic taste. When exposed to oxygen, this iron can become ferric iron, resulting in a rust-colored precipitation or film in the water. Overall, there are not great health risks associated with high levels of iron in drinking water. Rather, it is usually the aesthetics of the water that iron can affect.
Sources
Comprising approximately 5 percent of the earth's crust, iron is readily found in soil and water. As rainwater infiltrates the soil, iron can be dissolved and transported out of the soil and carried into groundwater. Deprived of oxygen, groundwater contains the soluble ferrous iron, which can be transported to underground reservoirs and other sources of drinking water. Iron is also used in coatings of many pipes used to transport water and over time, these coatings can begin to deteriorate, introducing excess iron into the water supply.
Iron in Your Body
Iron is used in the formation of many proteins in the human body, particularly those that carry oxygen through the bloodstream -- hemoglobin and myoglobin. There are no associated health risks with ingesting excess iron from drinking water. However, bacteria or other impurities that are potentially threatening can be absorbed onto iron-containing compounds. On average, drinking water supplies only about 5 percent of the daily iron requirements. Adults need between 8 and 16 mg of iron each day, and children need less than 10 mg, depending on age. The maximum amount of iron in drinking water, as suggested by the U.S. Environmental Protection Agency, is 0.3 mg per liter.
Effects on Drinking Water
When exposed to oxygen, dissolved iron can form precipitates in drinking water. When this happens, the water becomes cloudy with rust-colored tint. The EPA considers iron a secondary contaminant because there are no direct health effects associated with iron. Conversely, it is more considered a nuisance because of the change in color, taste and odor. Below 0.3 mg of iron per liter, water will remain clear and normal in taste. Once this level is exceeded, the water will have a strong metallic taste and will be discolored. At higher concentrations, the iron can actually lead to staining of clothes and household items.
Water Treatment
Corrosion control and conventional filtration can help reduce and prevent the introduction of iron into drinking water. By maintaining the pipes and equipment used to transport water, the chance of iron, and other contaminants, entering water supplies is reduced. Also, traditional filtering and the use of specialized filters known as activated carbon can help minimize iron concentrations. More expensive technologies, such as distillation and reverse osmosis are also highly effective at removing excess amounts of iron.
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