• Chlorine is commonly used disinfectant in water treatment.
• It can be employed directly as a gas or in the form of solution in water. It produces hypochlorous acids which is a powerful germicide.

Cl2  + H2O →  HOCL   +   HCL

• The death of micro organism result from chemical reaction of HOCL with the enzyme in the cell of the organism. since enzyme is essential for the metabolic process, death of micro organism result due deviation of enzyme.
• Clorinator is used for disinfection and about 0.3 to 0.5 ppm of chlorine is sufficient for fitered water.
• Advantages of chorine : It is effective and economical. It is stable, does not deteoriate on keeping and requires small space for storage. It can be used at high as well as low temperature. It does not introduce any impurity in treated water.
• Disadvantages of chlorine : The treated water should not contain more than 0.1 to 0.2 ppm free chlorine. If excess chlorine is added it produces unpleasant taste and odour and also irritation on mucous membrane. It is not effective at higher pH values.