A conference on environmental and health effects of water chlorination was convened in 1977: to improve communication between scientists and practitioners involved in studying the process and impact of water chlorination; to discuss pertinent research and developments; and to present data and conclusions emerging from the conference and note areas for further investigation. Areas of research on water chlorination and other forms of halogenation prominent in the 1970's were considered: (1) toxicity of active chlorine to aquatic life; (2) formation of chlorinated organic compounds in the process of chlorinating waste water effluent; (3) perdurability of chlorinated organic compounds in the environment and their accumulation in the food chain; and (4) formation of haloforms in the chlorination of drinking water. Sixty-six presentations addressed these research areas and other problems associated with water chlorination (primarily disinfection). Presentations are organized according to the headings of fresh water system and marine system chemistry, environmental effects in fresh water systems and marine systems, health effects, drinking water treatment, waste water treatment, cooling water treatment, industrial effluent, and regulations. Conference workshop summaries, a conference summary, and closing remarks are provided. References and an index are included.