Water Quality Assessment during Distribution System Flushing Events

Water distribution system flushing events are a weekly and often daily occurrence used to improve water quality. This study monitored water quality parameters associated with flushing events in a distribution system. Turbidity and pressure were continuously monitored for each flushing event, and 100 liter composite water samples were collected before, during and after each flushing event. The composite samples were analyzed for total coliforms, Escherichia coli, Pseudomonas aeruginosa, Aeromonas hydrophilia, Clostridium perfringens, and coliphage to statistically characterize microbiological water quality associated with the flushing event. The study identified portions of the distribution system that were rarely flushed, frequently flushed, and continuously flushed. Five flushing events were performed and monitored. The preliminary results of this study show turbidity is very sensitive to the hydrant value operations, and there is an apparent residual turbidity in the distribution system. Furthermore, indicator organisms (total coliforms and P. aeruginosa) were detected during the flushing events. The organisms could have been released from the system biofilm, and/or they could be indicative of finished water quality and regrowth potential.