Advice for Legionella Control During the COVID-19 Outbreak

Advice for Legionella Control During the COVID-19 Outbreak

During the current coronavirus pandemic focus has rightly been on the safety and well being of staff members and the general public with regard to tackling the spread of the virus and it becomes easy to lose focus on our general day to day priorities. However, as our work practices, movements and behaviour changes this can have a significant impact on aspects of the safety of our properties and this includes the risk associated with legionella bacteria. Health and safety law continues to apply and Dutyolders maintain a legal obligation to protect those in and around their properties from exposure to legionella bacteria. 

While controls in place may need to be adapted to changing circumstances, Dutyholders must still be able to demonstrate control of risk to a reasonably practicable level.

Legionella bacteria can grow and colonise water systems at temperatures between 20°C and 45°C, where a suitable nutrient source is available, and where turnover of water is low. As businesses increasingly move to a homeworking model during the coronavirus pandemic the demand for water in many commercial buildings will be significantly reduced. As demand is reduced the risk of low turnover and stagnation increases. With lower turnover we can also see increases in water temperatures as pipes warm to ambient levels. This risk can be further increased as the availability of maintenance staff and engineers is reduced through illness, isolation or travel restrictions.

Legionellosis (illness caused by legionella bacteria, including Legionnaires’ disease) is caused by inhalation of airborne water droplets containing high numbers of legionella bacteria. Those with a weakened immune system and other underlying illnesses hold a higher susceptibility to legionellosis. As the coronavirus pandemic escalates it is foreseeable that the number of individuals within society with a weakened immune system who are therefore susceptible to legionellosis will increase significantly. This is of particular concern in healthcare settings.


Hot and cold water systems

The main increased risk to hot and cold water systems caused by the ongoing coronavirus pandemic is associated with the reduction in demand for water as occupants stay away and work from home. Water usage should be monitored during this period and the volume of stored water in cold water storage tanks should be reduced where possible to ensure complete daily turnover is maintained. Weekly flushing regimes must be reviewed to ensure that all water services which receive infrequent use are included. For many buildings this may include most facilities.  


It is important that routine maintenance tasks continue as advised by the ACoP L8 and HSG274 Part 2 and maintenance practices should be reviewed and contingency plans updated to ensure that maintenance can continue consistently in the event usual maintenance staff are unable to fulfil their duties. In multi-occupancy buildings tenants should be contacted to ensure they continue to fulfil their obligations with regard to legionella control including at least weekly flushing of all infrequently used water services. In the event that maintenance practices cannot be fulfilled as advised additional control measures should be introduced. These may include use of biocides and/or microbiological sampling.

Where a building, part of a building or a water system is taken out of use: In general, systems are normally left filled with water and not drained down. The systems should be recommissioned as though they were new (see further details below) before being returned to use.


Return to Normal Operation

If buildings or water systems are isolated during the COVID-19 outbreak, the length of time involved may not have been known at the outset and control measures might not have been considered.  Staff may not have been available to flush to simulate usage.  Assess the risk – it is unlikely that buildings can simply be reopened with no additional measures. 

Start-up procedures for systems may need to be reconsidered before buildings can be reopened.  Consideration should be given to water system cleaning and disinfection and/or controlled flushing to mitigate the risk from prolonged stagnation.  Sampling may be useful to demonstrate effectiveness of control measures.


Evaporative cooling systems (Cooling towers and evaporative condensers)

During the ongoing coronavirus pandemic evaporative cooling systems must continue to be maintained in line with the guidance set out in the ACoP L8 and HSG274 Part 1. These systems are likely to require intervention to remain safe such as replacing chemical stocks, adjusting dosing levels and calibration of sensors.  

Serious consideration should be given to whether the systems are presently needed for comfort cooling purposes. If not, they should be pre-emptively shut down and suitably decommissioned.

If an evaporative cooling system cannot continue to be maintained in a safe and consistent manner, the system should also be shut down and decommissioned. 

The system(s) should then be recommissioned (including cleaning and disinfection) once normal service has resumed, and they are again required.


At Quantum Compliance we continue to monitor government advice regarding the coronavirus pandemic, and we will update our guidance as necessary. During any periods of restricted travel we will remain contactable to advise and assist. 

If you require further information or advice regarding legionella control or have concerns specific to maintaining the risks associated with legionella bacteria during the coronavirus pandemic please contact our Principal Water Consultant, Tom de Ronde,