The median iron concentration in rivers has been reported to be 0.7 mg/litre. In anaerobic
groundwater where iron is in the form of iron(II), concentrations will usually be 0.5–10
mg/litre, but concentrations up to 50 mg/litre can sometimes be found (6). Concentrations of
iron in drinking-water are normally less than 0.3 mg/litre but may be higher in countries
where various iron salts are used as coagulating agents in water-treatment plants and where
cast iron, steel, and galvanized iron pipes are used for water distribution.