CT - Chemical
Centralised treatment is shared by several households or at the village level and has different options of chemical water disinfection available to them than at the household level. The simplest and most common is through use of chlorine, although chlorine leaves a minor toxic residue, so other methods have been developed. One alternative is ozonation, as it leaves no harmful residues, yet is an expensive system to use. Today, combined systems can be found that use filtration, ozone, and smaller amounts of chlorine. De-fluoridation is also covered in chemical disinfection, as fluoride in water affects so much of the population in certain regions and is prevalent in their shared systems.