20 March 2020

Why to continue the flushing of infrequently used outlets during this period of upheaval?

Legionella preventative maintenance  PPM, Flushing Little-used Outlets, temperature checks, tank inspection

Many of our customers whilst recognising the important nature of the services we provide have asked for a document so they can share with colleagues the impact of halting all services whilst the building is out of use by the wider public, in particular the importance of flushing the system whilst unused. The below is a summary of the following document:

Flushing Information Pack

*COVID-19 is prevalent in comorbidity (The Lancet)

Now, more than ever, it's important to be mindful about Legionella control. Any illness that affects the respiratory system, if combined with COVID-19*, will likely have a high mortality rate and Legionnaires disease in one such illness.

“Where a building, part of a building or a water system is taken out of use, it should be managed so that microbial growth, including legionella in the water, is appropriately controlled.”

HSE - HSG274 Legionnaires’ disease Part 2: The control of legionella bacteria and cold water systems
Pg24. 2.5 - Buildings temporarily taken out of use (mothballing)

We have provide the following information with reference to the relevant parts of ACoP L8 and British Standards guidance regarding flushing:


  • You have to ensure a control method for managing the risk of legionella in your water system and in most instances flushing is an important and simple control method.
  • If you move away from flushing then a suitable alternative needs to be considered
  • Draining and decommissioning the system may be an option in some cases
  • In many cases you are unable to drain the system because other parts of the system still need to be operational
  • Leaving water to stagnate without flushing will encourage the bacteria to proliferate.
  • When bacteria is left to proliferate it can form a biofilm on all surfaces
  •  Once a biofilm is established it is very difficult to remove
  • This will inevitably result in additional disinfection works, sampling, remedial and possibly dosing equipment installed. These ongoing costs are likely to be significantly more than the cost of flushing.
  • During the period these areas are stagnant, increased levels of bacteria entering the other parts of the water system will not be prevented.
  • This will present a risk to any remaining residents or users on return to the building.
  • Although concerned with reducing the risk of COVID-19 this will potentially combine the possibility of legionnaires disease to the residents
  • This is true due to the fact that COVID-19 is prevalent in comorbidity

Flushing Information Pack


■ Legionella is a respiratory illness (pneumonia) and if co-concurring with influenza will lead to an outcome as detailed in this quote from a report in the lancet following investigations from the original outbreak in Wuhan - the presence and number of comorbidities is associated with poorer clinical outcome in patients with COVID-19

■ For further information on this please follow this link to a google search for Comorbidity and COVID-19 - comorbidity coronavirus COVID-19

■ HSE - HSG274 Legionnaires’ disease Part 2: The control of legionella bacteria and cold water systems

■ BS8558: Page 68, Guide to the design, installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages. Complementary guidance to BS EN 806

■ Legionella Control Association : Advice for LCA Members for Legionella Control During the COVID-19 Outbreak

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