Comprehensive overview paper: Essentials nutrients in drinking-water
Introduction
Most of the inorganic chemicals in drinking water are naturally occurring. They are acquired by the contact of water with rocks and soil and the effects of the geological setting, including climate (NAS 1977; WHO 1993; WHO 1996; WHO 1998). However, the chemical composition of drinking water is also affected by industrial, human and agricultural contamination and water treatment and distribution (NAS 1977; WHO 1993; WHO 1996; WHO 1998). Depending on water quality at the source, filtration, coagulation, and addition of chemicals to adjust pH and/or control corrosion treatments are employed (NAS 1977; WHO 1993; WHO 1996; WHO 1998; Letterman 1999). In addition, chlorination or chlorine dioxide and occasionally iodination may be used for disinfection, and fluoridation for the prevention of dental caries (White 1999: Backer and Hollowell 2000; IPCS 2002a). Leaching of minerals from contact with metal components in water treatment plants and plumbing materials occurs when pH and hardness of water are not adjusted. Main sources of dissolved metals include Cu from copper or brass plumbing system; Fe from cast iron, steel, and galvanised plumbing; Zn from zinc galvanised pipes; Ni from chromium-nickel stainless plumbing; Pb from tin-lead or lead solder and pipe; and Cd as an impurity in zinc galvanised pipes or cadmium containing solders (NAS 1977; WHO 1993; WHO 1996; WHO 1998; Alam and Sadiq 1989). Recently fortification of drinking water has been used in prevention of iron deficiency in children (Dutra de Oliveira and Nogueira de Almeida 2002) and to provide iodine in select populations (Elnagar et al. 1997).