In late 1984 the Metropolitan Water District of Southern California changed its primary disinfectant to chloramines to ensure that its member water agencies could comply with the 0.10-mg/L trihalomethane (THM) regulation. Subsequent taste and odor problems were determined to be an indirect consequence of chloramination, resulting from chloramines' lesser ability to oxidize odorous compounds released by certain microorganisms. The presence and possible sources of several off-odorants as well as various treatment techniques on THM levels in the distribution system are also examined. The effects of these treatment techniques on THM levels in the distribution system are also examined. Includes 29 references, tables, figures, photos.