Safe Management of Water Systems in Buildings During the COVID-19 Outbreak

Please be aware that The Health and Safety at Work Act still applies during this outbreak and Site Dutyholders must be taking reasonably practical steps to control risk from legionella throughout this time. Site Dutyholders implicated in an outbreak of Legionnaires’ Disease resulting from actions taken for COVID-19 precautions are not likely to have any exemption from prosecution.

Whitewater cannot make sweeping statements about what is critical, what can be deferred for a few weeks and what can be deferred for longer. The legal responsibility for legionella control lies with the Site Dutyholder, but Whitewater can provide advice to assist with compliancy situations. Each Site Dutyholder must make their own determination for each circumstance, but the following principles should be considered when making decisions on what to do to control legionella during the COVID-19 outbreak:

1.  The expectation for evaporative cooling systems is that they will be maintained as usual or switched off safely – this is essential.

2.  The expectation for water systems supplying critical services, e.g. hospitals, is that they will be maintained as usual – this is essential.

3.  Hot and cold water systems in buildings that are empty or with under occupancy must address the issue of stagnation:

a.  If the building is still partially in use, take additional measures to keep the remaining occupants safe:

  • If possible, drop stored water levels in tanks to maintain <24 hours storage
  • Flush to simulate use – weekly flushing may not be sufficient
  • Monitor temperature to ensure thermal gain in cold water is controlled
  • If fitted, consider temporarily increasing levels of potable water treatment dosing – consider other consequences of this such as corrosion and make the decision on balance of benefit
  • If controls are lost (temperature, biocide levels, etc.) the guidance in HSG274 is to sample for legionella weekly
  • Consider other short term measures to keep remaining occupants safe such as point of use filters at designated locations with other areas shut off
b.  Buildings that are temporarily shut down (mothballed) should follow the guidance in HSG274 Part 2 paragraphs 2.50-2.52, i.e.: –

  • Do not drain down pipework
  • If possible, remove sources of heat and external thermal gain
  • Lock-off, place signage on doors, and otherwise advise potential users that the system has been taken out of use
  • Have a plan in place for recommissioning the water system

For all of the work above there should be a task risk assessment in place to ensure operatives are working safely.

Recommissioning Water Systems

It is essential, when buildings reopen following the lifting of COVID-19 restrictions, that any water system is not simply put straight back into use. During the period of shutdown, it would be sensible to formulate a recommissioning plan for each water system to allow safe start-up and assurance to users that it is safe. Site Dutyholders can contact Whitewater to access competent help from service providers remotely during the period of restricted movement.

Any plan for recommissioning buildings must consider the safety of the operatives carrying out the work. It is foreseeable that the hazard present within water systems in this situation would be greater than normally expected. Reasonably practicable measures such as limiting aerosol, minimising exposure and use of RPE should be considered.

Evaporative cooling systems should already have robust start-up and shut-down procedures in place and the expectation is that these will be followed.

The minimum expectation for small, simple hot and cold water systems would be flushing through with fresh mains water. For larger buildings with tanks, showers, calorifiers and more complex pipework systems; the expectation is likely to be for more extensive flushing followed by cleaning and disinfection.

During flushing, all valves should be operated in the fully-open position so that any particulates can be purged. Float-operated or other restrictive valves are of particular importance as they may need to be manually opened to ensure clearing of particulates and prevent fouling. Where sufficient velocity to clear such particulates cannot be achieved, consideration should be given to removal of valves to enable an effective flush.

Where cleaning and disinfection is carried out, it is very important to monitor the decrease in disinfectant level (residual) over the course of the contact time. Loss of more than 40% active disinfectant could indicate influence of biofilm.

Where buildings have been vacant for some time and during warm weather, it is likely that some increase in microbiological levels and biofilm will occur. These water systems may require more than the standard disinfection protocol to be successful. Be prepared to expect some repeat disinfections to achieve a satisfactory result.

If this advice changes, Whitewater will update you accordingly.


For further advice or reassurance, please call 0118 9737616 or email us at