Flushing of healthcare water systems – a ‘necessary evil’?

The presence of Legionella in a water system is not a fluke, and its root cause is not lack of flushing. Flushing is a means not an end. So says Dr Nick Hill, Authorising Engineer (Water) at Water Quality London, and the former Chair of the IHEEM Water Technical Platform. Here he sets out the purpose, methods, benefits, shortcomings, and pitfalls, of flushing outlets such as taps and showers as part of the control process for Legionella in healthcare water systems.

Why do we flush taps, showers, and other parts of water systems? Generally, there are two circumstances which involve flushing of water:

This paper focuses on the latter circumstance. The reason for flushing water from parts of a system is to remove stagnant water because it contains, or it is suspected of containing, legionellae. All stagnant water in the water systems of buildings should be considered as potentially contaminated with legionellae. There are many people who believe that flushing is a method of temperature control, indeed almost a necessity to maintain cold water at a temperature below 20˚C, and to compensate for hot water system deficiencies to bring water at 55˚C to each outlet. Unfortunately, flushing is not an effective method of controlling water temperature.