Repeated attempts have been made to develop a corrosion index applicable to all waters. These attempts have shown that a series of indexes must be used to take into account the many different types of corrosion as well as all mitigating parameters. The Langelier saturation index, the momentary excess concept, the driving force index, the Casil index, the aggressive index, and Riddick's corrosion index are described. Parameters include hardness, alkalinity, pH, chloride, conductivity, total dissolved solids, color, phosphate, chlorine, and temperature, among others. Includes 19 references, tables, figures.