A one-year survey of halogenated disinfection by-products in the distribution system of treatment plants using three different disinfection processes

On a monthly basis, over a one year period, disinfection by-products (DBPs) were measured in raw water and in treated water at four locations in the distribution system of three water treatment plants that applied different treatment processes. DBP levels fluctuated as a function of water treatment practice (and variations therein) and the age and temperature of the water. Trihalomethane levels were higher in the summer than in the winter and increased in the distribution system with increasing distance from the plant. Levels of haloacetic acids and other DBPs were usually higher in summer than in winter but their levels did not increase consistently within the distribution system. After an initial increase, levels of dichloro- and trichloroacetic acids often decreased within the distribution system. No single sampling event captured the complete image of the behaviour of DBPs in drinking water. The authors recommend that in-depth studies be carried out to develop sampling strategies for DBPs.