Disinfection

Drinking water treatment always includes some form of disinfection. Drinking water might harbour many pathogenic species, each with its own infectivity, virulence and resistance to disinfection. Individual monitoring of all potential organisms is clearly impractical. The problem is simplified by considering the contaminants in their conventional microbiological classes, namely viruses, bacteria and protozoa. For each group, one or more reference organisms are singled out for posing the largest threat. If ammonia is added to water with free chlorine in the right proportion, monochloramine is formed which is also a disinfectant. Although it is not as effective as free chlorine, it has the advantage that it is more stable to maintain a residual in the water for a longer time. Rand Water, for example, uses monochloramine after primary disinfection to maintain sufficient residual of disinfectant over its vast supply area where it may take a week for treated water to reach the furthest points.