How lockdowns can cause water stagnating and hence growth of Legionella

In 2020 we went through an unprecedented situation with hundreds if not thousands of public as well as private buildings left unoccupied. Unused buildings generate a health risk once they are back open. It is unlikely that we will go back to a solid lockdown where so many buildings were shut, but in case something similar happens again, building owners need to be vigilant over possibly fatal Legionella at buildings left vacant due to COVID-19.

With the confinement and lockdown, a number of buildings were empty or experiencing minimal occupancy and, as a consequence, domestic water systems within these buildings were potentially a source of Legionella.

Unoccupied buildings run the risk of water stagnating and therefore growth of Legionella, providing conditions where dangerous Legionella bacteria can proliferate.



Experts urge property owners, tenants and managers across the region to be aware of the risks and take the necessary actions, in case similar lockdowns would be necessary again.


Be aware and vigilant

Authorities have issued warnings over possibly fatal Legionella outbreaks at offices and other types of buildings left unoccupied due to COVID-19. The coronavirus crisis has truly caused unprecedented building closures. Many have near zero or reduced occupancy and face an increased risk of exposure to Legionella bacteria. This is why we are encouraging building owners, managers as well as landlords to be aware and vigilant of their legal obligations and to consider Legionella training for the members of their staff.



Some of the most important risks of potential exposure to Legionella happens when a lockdown actually ends. It is crucial that the water systems are made safe prior to reopening and reoccupation.

It is not a must to drain down mothballed systems since this does not totally eliminate the existing risk. However, in all circumstances the flushing of water needs to be exercised with caution as there will be potential for stagnant water to form aerosols containing the bacteria.

Legionella risk assessments will also identify the risks and control measures needed. If you are in doubt, an expert water treatment service provider should be consulted.

Legionnaires’ disease is a pneumonia caused by Legionella bacteria. It is generally contracted by breathing in mist from water that contains Legionella bacteria. Exposure to this bacteria can be caused by inhaling small droplets of water from items like air conditioning. Symptoms may include a cough, fever, high temperature, muscle pains, diarrhea, mental confusion and headaches.


Ways to address Legionella risk in unoccupied buildings amid coronavirus

  • Review the risk assessment and written control scheme, especially with current occupancy in mind
  • Identify low use outlets and set up a flushing plan
  • Identify if occupants may be more susceptible to Legionella bacteria and control the risk
  • Guarantee flushing of low or near zero use outlets on a regular basis
  • Make sure routine water temperature testing records are maintained
  • Make sure water systems that have been left stagnant are recommissioned as if new

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