Further Advice for Legionella Control During The COVID-19 Outbreak

Quantum Compliance have issued general advice on management of water systems during the Covid-19 outbreak on 23rd March. This advice note provides further, more specific and practical advice for hot and cold water systems, and evaporative cooling systems.

Hot and Cold Water Systems

Low Occupancy

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

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. (See Hygiene Flushing below).
  • Monitor temperatures 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.
  • If controls are lost (temperature, biocide levels, etc.) the guidance in HSG274 is to sample for legionella on a weekly basis.
  • Consider other short term measures to keep remaining occupants safe such as point of use filters at designated locations with other areas shut off.


Buildings that are temporarily shut down (mothballed) should follow the guidance in HSG274 Part 2 paragraphs 2.50-2.52:

  • 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 detailed above, there should be a task risk assessment in place to ensure operatives are working safely.

Recommissioning Hot and Cold Water Systems

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

In all cases where systems are being recommissioned, it is sensible to have evidence to prove/reassure that the recommissioning process has been effective. Legionella sampling to BS7592 should be considered for recommissioning plans to validate the effectiveness of the process.  As per HSG274 part 2, samples should be taken 2-7 days following recommissioning and not on the day of disinfection.

Hygiene Flushing of Hot and Cold Water Systems

All outlets which are not in regular use (generally taps and showers) should be subject to a minimum of weekly flushing. This will need to include Landlord and Tenant services.

This procedure has to be sustained and logged.

All infrequently used equipment within a water system (i.e. not used for a period equal to or greater than seven days) should be included on the flushing regime.

Flush the outlets until the temperature at the outlet stabilises and is comparable to supply water:

  • Cold Water Service: within 2°C of the CWS Tank nearest outlet and < 20°
  • Hot Water Service: >50°C or < 20°C if no longer heated. (Note keep circulating pumps running)

If thermometer equipment is unavailable then flushing outlets for 5 minutes is recommended, however recording temperatures is preferable to demonstrate compliance.

Toilet cisterns should just be flushed once a week, as should urinals.

Where the hot and cold water is not used for a prolonged period and has not been flushed as recommended, for example, this could be as little as two or three weeks, but will depend on the ambient temperature, the condition of the water system, potential for exposure to aerosols and the susceptibility of users should be considered in a specific risk assessment. Hot and cold water services should be cleaned, flushed and disinfected, as specified in PD855864.

Evaporative Cooling Systems (Cooling Towers and Evaporative Condensers)

Evaporative cooling systems should be maintained as usual or switched off  –  there is no leeway in this.

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

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, tom.deronde@qcompliance.co.uk