Repeated conventional flushing to improve water quality in a full-scale distribution system

One of the primary ways utilities prevent and address water quality concerns in distribution systems is via regular hydrant flushing, yet rigorous research to evaluate the impact of full-scale flushing programs is limited. This study employed time-series and correlation analyses to evaluate the efficacy of a utility's five-month repeated conventional flushing program to reduce nitrification and improve disinfectant residual concentrations in the distribution system. Short-term water quality improvements during flushes were common across the 16 locations flushed, but lasting improvements were inconsistent as demonstrated by continued nitrification and heterogeneous water quality changes. Flushing frequencies and flow rates may need to be tailored to individual sites, even when similar water quality challenges exist. Water quality monitoring data and related analyses helped to prioritize flush sites, maximize efficiency during and between flushes, and inform decisions to implement additional interventions.