Bleaching powder is used for disinfecting drinking water give reason.

Addition of bleaching powder to water called chlorination and is a part of drinking water treatment process due to its important disinfectant properties.

Bleaching powder contains sodium hypochlorite, when applied to water, each of these forms “free chlorine,” which destroys pathogenic (disease-causing) organisms.

In addition, chlorination offers a number of benefits including:

Reduces many disagreeable tastes and odors;

Eliminates slime bacteria, molds and algae that commonly grow in water supply reservoirs, on the walls of water mains and in storage tanks;

Removes chemical compounds that have unpleasant tastes and hinder disinfection; and 

Helps to remove iron and manganese from raw water.

Only chlorine-based chemicals provide “residual disinfectant” levels that prevent microbial re-growth and help protect treated water throughout the distribution system.