The major component of the metal salts used in the wastewater treatment process is usually aluminium or iron. Iron as a basic material is produced from ores such as magnetite and hematite, aluminium from bauxite ore. However, many of the products used in water treatment are made from by-products of other industrial processes.

The metal salt products can be solids or aqueous solutions. However, most of them are in liquid form, as sulphates or chlorides. The metal salts and their aqueous solutions are used in waste water treatment mainly as coagulants (see coagulation) and for the precipitation of phosphates. Metal salts are also used in the dewatering of sewage sludge to achieve a higher dewatering result, to avoid the formation of magnesium ammonium phosphate scaling or to improve the separation of the filter cake in chamber filter presses.

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