Demonstrating the Effectiveness of Flushing for Reducing the Levels of Legionella in Service Lines and Premise Plumbing


Flushing is a common approach used to control Legionella levels in building plumbing systems, but there are no standard or widely accepted approaches. The effectiveness of flushing is likely to vary with the flush water temperature and type, concentration of residual disinfectant in the flush water, flushing flow rate (i.e., fluid velocity), and flushing time.

Project 5033, “Demonstrating the Effectiveness of Flushing for Reducing the Levels of Legionella in Service Lines and Premise Plumbing,” evaluated the efficacy of flushing as a corrective action for reducing Legionella levels in buildings’ cold- and hot-water systems. Specific research questions concerned the roles of flushing flow rate, flush water temperature, presence/absence of residual disinfectant (i.e., chloramines), and flushing frequency on Legionella levels in the water and biofilm of building plumbing systems.

In this webcast, presenters will discuss the findings and results of this project, including recommendations that are based on easily measurable water quality parameters, such as temperature and/or chlorine residual. This approach ensures that the flushing procedure can be implemented with ease by operators and building managers, making it accessible and practical for real-world application. 

Cynthia Hallé, PhD 
Department of Civil and Environmental Engineering, Norwegian University of Science and Technology, Associate Professor
Department of Building and Environmental Technology, Norwegian University of Life Science
Organization, Adjunct Associate Professor

Raymond M. Hozalski, PhD
James L. Record Professor, Department of Civil, Environmental, and Geo- Engineering
University of Minnesota

Michael Waak
Researcher, Environmental Engineering, Department of Infrastructure
SINTEF, Norway

Grace Jang, PhD
Research Program Manager
The Water Research Foundation