The physical processes of the treatment plant remove a large percentage of bacteria and other microorganisms, especially by sand filtration. However, many bacteria and viruses still remain in water – even at low turbidity levels. It is therefore essential to disinfect water to prevent water-borne diseases from spreading by pathogens (disease-causing micro-organisms) in water.

Disinfection of water entails adding the required amount of a chemical agent (disinfectant) to the water and allowing contact between the disinfectant and particles for a pre-determined period of time under specified conditions of pH and temperature. Other methods of disinfection include boiling water or irradiation with ultra-violet light.

Midvaal applies chlorine for disinfection purposes. Chlorine is a strong oxidising agent and it reacts and oxidises some of the essential metabolic systems of microorganisms, thereby inactivating or destroying them.

Chlorine gas is purchased from reputable suppliers in South Africa, and contained in steel drums of roughly 925kg capacity. It is extracted from these pressurised drums with special chlorination equipment under regulated conditions and dosed into the treated product as the final treatment step. It is imperative that the chlorination step in uninterrupted and that sufficient chlorine is dosed at all times for adequate disinfection of potable water