Activated carbon is useful in drinking water treatment because it acts as an adsorbent , and can effectively remove particles and  organics from water. These organics are of great concern in water treatment because they react with many disinfectants, especially chlorine.
 

The use of granular Activated Carbon in wastewater treatment systems is a proven process for removal of organic compounds. As a tertiary treatment method, carbon adsorption and regeneration have been used to process domestic wastewaters contaminated with industrial wastes of organic origin as well as biologically treated waste waters. Activated Carbon, when contacted with water containing organic material, will remove these compounds selectively by a combination of adsorption of the less polar molecules, filtration of the larger particles, and partial deposition of colloidal material on the exterior surface. The quantity of Activated Carbon required will depend upon the degree of contamination.