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Legionnaires’ Disease: Reopening Safely After Lockdown

This bulletin consists of a transcript of a guidance note for policyholders drafted for a client of RiskSTOP Surveys.

Consultants will be aware of the risks associated with Legionnaires’ disease and the potential increased risk arising from stagnation in the water system as a result of low usage during lockdown. Consequently, there will be many businesses for which a review of the legionella risk assessment will need to be undertaken and an action plan formulated for safe start-up (for which an item has been added to the standard risk improvement wordings).   

When reopening premises after lockdown, it is vitally important that water systems are not returned to use without fully considering the risks of Legionnaires’ disease and the increased risk which may have been created as a consequence of lockdown. Also, there is the potential for an increased number of people to be susceptible to Legionnaires’ disease due to a compromised respiratory system during or after infection with COVID-19.



Legionnaires’ disease is a type of pneumonia which can cause serious respiratory illness. It can occur when tiny droplets of water (aerosol) containing Legionella bacteria are breathed into the lungs of susceptible people. Preventing Legionnaires’ disease is typically achieved by limiting the growth of Legionella in building water systems.

Legionella bacteria will inevitably enter man-made water systems and the degree of risk it poses will vary. All hot and cold water systems need to be considered, including those at: retail outlets; hairdressers; beauty salons; offices; hotels; gyms; sports clubs; golf clubs; hotels; pubs; clubs; restaurants; camp sites; volunteer-run premises and anywhere that has a water supply which has been shut down or is experiencing restricted use.

This guidance is intended to assist employers, the self-employed and persons in control of premises, such as landlords, all of whom have a legal duty to protect people by identifying and controlling the risks associated with legionella. It is focused towards smaller hot and cold water systems and is provided on the basis that organisations will already have suitable control measures in place as part of a risk management programme.

Where specialist water systems are present such as swimming pools, spa pools and industrial premises with, for example,  cooling towers and evaporative condensers, the advice from a competent specialist consultant should be sought.  



Prior to reopening following lockdown or a period of reduced occupancy, it is essential that the legionella risk assessment is reviewed and a plan formulated to allow safe start-up. Any plan should consider the competency and safety of persons carrying out the work. The hazards from legionella bacteria are likely to be greater than expected under normal conditions requiring measures such as limiting the production of water droplets (aerosol) and minimising exposure to droplets, for which the use of respiratory protective equipment may be considered necessary.

Key measures to be undertaken prior to reopening could include:

  • Flushing through simple hot/cold water systems for several minutes with fresh mains water. (The process of flushing can generate water droplets and requires safe planning such as running taps at low velocity or submerging shower heads under a container of water.)   

  • Increasing the temperature of hot water systems to above 60°C  through to all hot water outlets.  (Increasing the water temperature to 60°C and above can result in a scalding risk).

  • Flushing through larger hot/cold water systems, including those with tanks, showers, calorifiers etc. for a significant period of time.

  • Ensuring that the system is capable of delivering  water at safe temperatures by checking temperatures ahead of reopening.

  • Undertaking a chemical or thermal disinfection of the water system.

  • Performing microbiological sampling for Legionella bacteria.

All control measures undertaken should be formally recorded.

It is important to state that where water systems are under poor control, this guidance may be insufficient to achieve safe reopening and in these circumstances the risk assessment services of a specialist consultant are likely to be required.

For all services appertaining to the assessment and control of Legionnaires’ disease, it is recommended that service providers are chosen from registered members of the Legionella Control Association.



Detailed information relating to Legionnaires’ disease can be found, for example, in the following HSE publications, all of which are freely available online:

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