Results of this study, although preliminary at this time, indicate that for the majority of pipe types and sizes studied, unidirectional flushing appears to be the most practical and effective means of biofilm control for a distribution system. As the ecology of distribution system biofilms is extremely complex, more than one type of microbial monitoring system is required to obtain the maximum amount of information. Microbial data needs to be interpreted together with the hydraulic phenomena occurring during the mains flushing program to give an accurate account of the flushing event and degree of mains cleaning. This information can then be used to improve flushing programs to maximize distribution system maintenance activities and to maintain water quality within the system. The costs of unidirectional flushing are considerably lower than for conventional flushing or water line pigging, making it a viable program for many water utilities.