Disinfection of water is the process of destroying or inactivating disease-causing organisms in water supplies. Although it is not as thorough as sterilization, which completely destroys all living organisms, disinfection makes the water safe for drinking and cooking. The most common method of disinfecting community water supplies is chlorination. Hypochlorite, rather than chlorine, is commonly used for small water supply systems. This technical note gives information about disinfection in rural community water supply systems in developing countries. Topics include: what is disinfection; effectiveness; types of disinfection for small systems; methods of feeding hypochlorites in a water systems; and costs of disinfection. on lessons learned, notes that most disinfection methods for small systems have not worked on a sustained basis due to such factors as lack of community education and operator training, an undependable supply of chemicals and spare parts, or an inappropriate technology.