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 completed study monitored water quality parameters associated with 12 flushing events in a distribution system. Turbidity and pressure were continuously monitored for each flushing event, and 100-liter large volume water samples were collected before, during and after each flushing event. The 100-liter samples were analyzed for total coliform, fecal coliform, E. coli, heterotrophic plate count, P. aeruginosa, A. hydrophilia, C. perfringens, and coliphage to statistically characterize microbiological water quality associated with the flushing event. The study identified portions of the distribution system that had never been flushed, that were rarely flushed, that were regularly flushed, as well as locations at low and high elevations. The study results showed turbidity is very sensitive to fire hydrant valve operations, large volume water samples better represent the quality of water in the system than small volume samples, and total coliforms, P. aeruginosa, and A. hydrophilia analytes were found in pre flushing and flushing water samples which are indicative of the finished water quality and are an indication of regrowth potential in the distribution system.