"Corrosion is a natural process that occurs when metals react with oxygen and form metal oxides. All water contains some dissolved oxygen and is therefore somewhat corrosive. The rate of corrosion depends on many factors including the water’s pH, electrical conductivity, oxygen concentration, and temperature. In addition to corrosion, metals dissolve when the water is extremely low in dissolved salts and in the presence of certain water-borne ions. This process causes the plumbing material to gradually dissolve. Though corrosion and dissolution are fundamentally different, the result is similar and they are generally discussed as corrosion." (McFarland, n.y.)
McFarland, M, Provin, T., and Boellstorff, D. Drinking Water Problems: Corrosion. University of Texas A&M AgriLife Extension. E-616 7/12.