Disinfection is a process of killing all pathogens. Sterilisation is a process in which the total and complete destruction of all types of bacteria takes place.

Safe water means

(a) water free from bacteria

(b) water aesthetically acceptable

(c) water free from excessive minerals and poisonous matter.

Thus, the process of killing pathogenic bacteria from water and make it safe for use is called disinfection. The chemicals or substances used for disinfection is called disinfectant.

DISINFECTING AGENTS

The various agents of disinfection of water are as follows :

Physical Agents

• Heat

•Light (natural sun radiation, artificial)

Chemical Agents

•Potassium permanganate (used in hospitals)

•Ozone, $O_3$$0_2$ + O Nascent oxygen

•Chlorine and its compounds

•Bromine (used in swimming pools)

• Iodine (used in tablet form)

• Phenol and phenolic compounds

• Acids and alkalies

• Heavy metals and related compounds

• Dyes

• Soaps and synthetic detergents

• Hydrogen peroxide

• Quaternary ammonium compounds.

Historically, the disinfectant widely used is chlorine. Chlorine may be applied as a gas (C$l_2$) or as the salts of hypochlorite [Ca(OC1$)_2$, NaOCI]. Bromine and Iodine are occasionally used for swimming pool water.

Ozone is produced on site by passing pure oxygen, or dry, clean air in a high strength electric field. Ozone is highly effective disinfectant. Its use now-a-days is increasing. Highly acidic and alkaline water can also be used to kill pathogenic bacteria.

Irradiation with ultraviolet light (UV) has also been used for disinfection. Although it provides no residual disinfectant, UV is effective in inactivating bacteria and viruses.

The use of electron beam as a method of disinfection is now under active research in the United States. Gamma-ray irradiation is used in Germany and along with the electron beam, is in active research in Japan.