Chlorine kills most disease causing organisms and requires short to moderate contact times. It does not provide adequate protection against parasites such as Giardia and Cryptosporidium. To remove these parasites and their cysts it is recommended that water be first passed through a filter with 1 micron or smaller pore size and then chlorinated. Iodine disinfection of drinking water should be reserved for emergency or occasional use because ingestion of too much iodine may be harmful.
Ultraviolet light (UV) devices are effective against bacteria, viruses and when properly sized and designed, against parasite cysts. A pre-filter may need to be used to reduce turbidity before water is exposed to UV light.
Chlorinators and UV devices are used when it is necessary to disinfect water that serves a dwelling.
Ceramic or glass filters handle smaller amounts of water, for example when just one tap is to be used for drinking or cooking. They can remove bacteria and parasites. They are not capable of removing viruses.
Distillers and ozonators require electric power and sufficient space for installation. The boiling process used in distillation will kill bacteria, viruses, and parasites. Ozonators produce small quantities of ozone, a strong oxidizing agent that is effective in killing pathogens over a short period of time. Unlike chlorine, ozone does not provide significant residual disinfection.
Iodine disinfection of drinking water should be reserved for emergency or occasional use because ingestion of too much iodine may be harmful.
Health Canada - Water Treatment Devices for Disinfection Of Drinking Water