Legionella: Guidance for Re-Opening and Re-Occupation of Buildings: Hot and Cold Water Services

Quantum Compliance has issued general advice on management of water systems during the Covid-19 pandemic on 25th March. This was followed by a further advice note on 3rd April, with more specific and practical advice for hot and cold water systems, and evaporative cooling systems.

Feedback from Legionella risk assessments, carried out since the official lockdown at the end of March can be found below.

The Legionella Control Association (LCA) has issued guidance on Reopening Buildings, which is summarised below.

  • Simply reopening a building that has stood idle, without addressing the safety of its water system is unacceptable and is likely to be in breach of the law.
  • If Dutyholders are not able to put in place a proper recommissioning process to use the water system safely, they should not reopen the building.
  • Buildings that have remained empty with static water systems, or those that have been subject to limited flushing that does not represent normal usage, will require recommissioning. Those that have remained in normal use or where flushing has approximated normal usage (evidenced) may still require additional control measures.
  • Recommissioning a building water system should be appropriate for the risk. For very simple buildings flushing alone may be sufficient but for most buildings some form of disinfection is likely to be needed. In the worst cases, repeat disinfection and extensive cleansing flushing may be required to clear contamination.

A Flow Chart has been created by the LCA to be used in the risk assessment process and is available by clicking on the following link:


Feedback from Legionella Risk Assessments undertaken during the COVID-19 Pandemic

The below provides feedback from the dozens of risk assessments and audits completed since the Covid-19 lockdown period and refreshes the key elements.

During the Covid-19 low occupancy period it is critical that we follow the ACOP and Technical Guidance from the HSE and LCA, regarding the management of low occupancy in commercial buildings to:

  • Protect those who remain within the buildings and use the water systems from Legionella exposure. (For example, Security, Maintenance and Soft Services Personnel, plus small numbers of Tenant staff still using office space and services).
  • Avoid having to disinfect and sample water systems prior to full building re-occupation, which will inevitably be disruptive and may cause delays in re-occupation.

Hot and Cold Water Systems

Low Occupancy

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

  • If the building is still partially in use take additional measures to keep the remaining occupants safe:
  • Flush to simulate use – weekly flushing may not be sufficient. (See Hygiene Flushing below)
  • Monitor temperature to ensure thermal gain in cold water is controlled.

Feedback from Risk Assessments conducted so far

In most instances low use outlet flushing has been instigated, however those carrying out the flushing were not carrying out and/or recording correctly.

For example, one line in the flushing log indicating ‘all communal outlets’ flushed for unspecified time with no record of temperatures does not follow the guidance.

Why do we require temperature recording during low use outlet flushing?

  • To demonstrate thermal control, i.e. Hot Water > 50°C and Cold Water < 20°C.
  • Without this it is impossible to determine whether the outlet has been flushed for the correct period (i.e. comparable to supply water), in which case the flushing period maybe too short (resulting in water stagnation hazards/thermal gain issues) or too long, resulting in Hot Water Vessels dropping below required storage temperatures.
  • Outlets within tenanted areas are not being flushed by the Managing Agents M&E contractor. In some circumstances the risk from this is low-medium (i.e. some offices only have a kitchen with POU water heater on each floor), in others the risk is much higher as there are toilets and showers within the tenanted areas, which form a significant part of the building’s water system. Our feedback so far is that there are few additional flushing measures being taken by tenants’ service providers.

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 must 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, condition of the water system, potential for exposure to aerosols and the susceptibility of users 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 and there is no leeway on 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.

Feedback from Risk Assessments conducted so far:

 Unsurprisingly, cooling demands are much reduced which will affect the Cooling Tower operation in different ways depending on how these are set to operate, generally through the BMS.


  • You will need to update the system operation details in the logbook to reflect the reduced circulation pump and fan times during the Covid-19 low occupancy period.

The updated system operation details need to confirm arrangements are in place to ensure that treated water circulates through the entire system (this should be monitored, and records kept as normal). The system, including the fans, should run for long enough to distribute the treated water thoroughly.

 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