The type of chemicals added to the water in the treatment process has to comply with nationally approved standards for water purification for human consumption. The quality of raw water at the time of abstraction determines the amount of chemicals to be added to treat the water to the required standard. At Midvaal, the following chemicals are used.

Type of Chemical Example Purpose
Flocculants** Ferric chloride, aluminum sulphate Coagulates suspended particles into floes
Flocculant aid Anionic and cationic polymers Assists with removal of very fine particles and are used mainly during rainy seasons when high turbidity water is experienced.
Stabilization/pH correction Hydrated lime To ensure that the treated water is neither scale forming nor corrosive
Oxidation Ozone gas Removes algae, dissolved metals like iron and manganese, removes color, tastes and odours
Disinfection Chlorine gas Kills harmful bacteria and other micro-organisms

** Flocculation involves the stirring of water to which a coagulant has been added at a slow rate, causing the individual particles to “collide” with each other and with the floes formed by the coagulant. The destabilized individual colloidal particles are agglomerated and incorporated into the larger floc particles