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Legionella risk and the COVID-19 outbreak

Risk & Analytics|Corporate Risk Tools and Technology|Risk Management Consulting
COVID 19 Coronavirus

By Mike Conde | July 14, 2020

This risk insight examines how to identify and control risks associated with legionella during COVID-19.


As the government slowly begins to ease restrictions following the COVID-19 pandemic many organisations are thinking about how to continue working from home safely and effectively and in some cases, how to return to the workplace.

If your building was closed or will have reduced staff occupancy when you reoccupy it, water stagnation can occur in your water systems due to lack of use. This in turn can increase the risks of Legionnaires’ disease - a potentially fatal form of pneumonia caused by the bacterium Legionella pneumophila and related bacteria. Although common in natural water sources such as rivers, lakes and reservoirs, they may also be found in purpose-built water systems such as cooling towers, evaporative condensers, hot and cold-water systems and spa pools1.

Employers, the self-employed and people in control of premises, such as landlords, have a duty to protect people by identifying and controlling risks associated with legionella. This is also an important factor to be considered when planning to return to the workplace.

Applicable Health and Safety Law

  • The Health and Safety at Work etc Act 19742 extend to risks from legionella bacteria that arise from work activities.
  • The Management of Health and Safety at Work Regulations 19993 includes the requirements for conducting risk assessments.
  • The Control of Substances Hazardous to Health Regulations 20024 includes the prevention and / or control of risk from bacteria, like Legionella.
  • The Approved Code of Practice: Legionnaires’ disease5: The control of Legionella bacteria in water systems (L8) contains practical guidance on how to manage and control the risks in your system.

What you need to do

If your water system has remained in regular use you must continue to maintain the appropriate control measures outlined in your maintenance scheme. This will prevent legionella growth or maintain it at safe levels.

If your water system hasn’t been used for a while due to a workplace closure or has been used much less due to fewer persons occupying your workplace, you should review your legionella risk assessment and manage the legionella risks when you reinstate your water systems or some types of air conditioning systems.

You will probably require specialist advice to help you review your risk assessment and identify and implement the controls necessary for legionella. If you are unable to get specialist help you must consider stopping/shutting down water systems.

Hot and cold-water systems

You should flush all of your hot and cold-water outlets before reoccupying the premises to remove any stagnant water that’s has been sitting in pipes etc. If you can’t do this, you should clean and disinfect the water systems before use. Shower heads should also be stripped, cleaned and disinfected before use, too.

Cooling towers and evaporative condensers

If you have a cooling towers or evaporative condensers and they have been or will remain out of operation for:

  • Less than a month – You should isolate the fans and circulate biocidally-treated water around the system for at least an hour once per week.
  • More than a month – You should drain down the system, clean and disinfect it.

If either of the above didn’t take place when you first stopped using the system you should drain, (if required) clean and disinfect it, before refilling and returning it to normal operation.

Air conditioning units

If your workplace or part of the workplace has been closed for an extended period and has air conditioning units that have a source of water that can generate aerosol that haven’t been used in a while, you should assess the risks of legionella being present within them before restarting. When you review your risk assessment, decide what the risks are for your units and if you need to clean and disinfect them before they are turned on.

Small wall or ceiling-mounted units with closed cooling systems aren’t usually considered a risk. Larger units may present a risk if they have improperly drained condensate trays, or humidifier or evaporative cooling sections where water can stagnate, becoming a reservoir for bacteria to grow.

Commercial spa pools and hot tubs

If you use commercial spa pools and or hot tubs, you must maintain the existing control regimes set out in the Maintenance Scheme. If they are not being used, they should be drained, cleaned and disinfected. This should be done again before they are put back into use.

Methods of control

Temperature control is the main form of control used in hot and cold-water systems. Once up and running the required temperature checks should be conducted initially and then as per the maintenance scheme for your water systems. Where necessary steps should be taken to achieve the required temperatures.

Biocides are sometimes used as an alternative method of control in cooling towers and evaporative condensers. Other chemicals such as corrosion and scale inhibitors are used too. If you are struggling to source the chemicals, you usually use then alternatives may be available in some cases. Talk to your supplier for more information or contact HSE.

Physical methods can also be used for cooling tower control such as hydrodynamic cavitation, ultrasonic cavitation, TiO2 Advanced Oxidation Process but does not suit all systems. No chemicals are required using this method.

Replacement of smaller cooling towers and evaporative condensers with dry coolers or dry/wet coolers is another possibility. They run with little or no chemicals but are expensive.

Changing method of control and the risks to operators

If you decide to change your method of control you must review your risk assessment and increase your monitoring during the commissioning stage of using new controls. Operators may be exposed to additional or different risks. For example, moving from an oxidising biocide to Isothiazoline may introduce a new skin sensitisation risk.

Personal protective equipment (PPE) required for cleaning water systems

If you need to clean a water system before restarting it, it’s likely that respiratory protective equipment (RPE) will be needed by the operatives. The RPE must adequate, suitable and at least PF20. The RPE selected should be based upon your risk assessment and options include:

  • a reusable half-mask or full-face respirator fitted with a P3 filter
  • a powered respirator and hood class TH2 or 3
  • a powered respirator and close-fitting full-face mask class TM3
  • an air-fed hood or full-face mask supplied with breathing quality air

Additional sources of information

For further information or guidance, please contact your Willis Towers Watson representative.


Each applicable policy of insurance must be reviewed to determine the extent, if any, of coverage for COVID-19. Coverage may vary depending on the jurisdiction and circumstances. For global client programs it is critical to consider all local operations and how policies may or may not include COVID-19 coverage.

The information contained herein is not intended to constitute legal or other professional advice and should not be relied upon in lieu of consultation with your own legal and/or other professional advisors. Some of the information in this publication may be compiled by third party sources we consider to be reliable, however we do not guarantee and are not responsible for the accuracy of such information. We assume no duty in contract, tort, or otherwise in connection with this publication and expressly disclaim, to the fullest extent permitted by law, any liability in connection with this publication. Willis Towers Watson offers insurance-related services through its appropriately licensed entities in each jurisdiction in which it operates.

COVID-19 is a rapidly evolving situation and changes are occurring frequently. The information given in this publication is believed to be accurate at the date of publication shown at the top of this document. This information may have subsequently changed or have been superseded, and should not be relied upon to be accurate or suitable after this date.








Dip NEBOSH, CMIOSH, Health & Safety Practice

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