Flushing as a Control Measure for Legionella spp.: Impacts of Water Age, Chloramine Disinfection, and Elevated Temperature

High Resolution Image Download MS PowerPoint Slide Pilot-scale experiments were used to examine how hot-water temperature, chloramine disinfection, and pipe material (copper or PE-Xa) influence the effectiveness of two flow-based interventions─high-flow flushing vs showering─in controlling total bacteria, Legionella spp., and Vermamoeba vermiformis in premise plumbing. Flushing (ca. 16 L/min for 5 min) and showering (ca. 7 L/min for 8 min) both temporarily reduced bacterial concentrations by removing accumulated planktonic biomass. However, total bacteria rebounded within 1–4 days after a flush or shower, regardless of the presence of chloramines (1 mg/L Cl 2 ). In the absence of chloramines, Legionella spp. ssrA gene concentrations increased over 3–10 days following flushing or showering, whereas chloramines suppressed Legionella spp. for >10 days despite completely decaying within hours of water use. Without chloramines, hot-water flushing at 49 or 60 °C provided little additional control of Legionella spp. as compared to cold-water flushing. V. vermiformis concentrations decreased temporarily following water use, independent of disinfectant or temperature. Flushing was more effective than showering at removing Legionella spp. from biofilms, while pipe material had limited influence in this pilot-scale system. Overall, the results demonstrate organism-specific recovery dynamics and highlight the role of chloramines in prolonging the suppression of Legionella in premise plumbing.