It is important that Legionella management remains robust and you continue to dynamically address the risks within your buildings as they reoccupy, rather than just reverting back to previous regimes.

Both the Health and Safety Executive (HSE) and the Chartered Institute of Environmental Health (CIEH) (amongst others) have produced guidance on the subject, indicating (in the words of the HSE):

  • “If the water system is still used regularly, maintain the appropriate measures to prevent legionella growth.”
  • If your building was closed or has reduced occupancy during the coronavirus (COVID-19) outbreak, water system stagnation can occur due to lack of use, increasing the risks of Legionnaires’ disease. Review your risk assessment and manage the legionella risks when you:
    • reinstate a water system or start using it again
    • restart some types of air conditioning units”

The CIEH document “Legionnaires’ disease: lockdown risks and reopening safely” “Advice on reopening” pages 3 and 4 is also a good reference. These are linked at the end of this guidance.

In assessing how best you manage your buildings and their water systems and services during this change, we have provided you with the following advice.

All water systems

Just as with adjusting to managing ‘empty’ buildings, there is no blanket approach to managing re-occupation that will fit all circumstances or individual sites. Some buildings will have continued with their ongoing PPM schedule, amending it as necessary to address the risks; other sites may have simply been ‘abandoned’ and the water services left operational.

Your site specific, water management system and risk assessment are the key documents you need to initially review. Continue to focus on any high risk areas you are aware of.

Owners and operators of water systems have a duty to keep them safe, which requires a suitable and sufficient assessment of the risk associated with Legionella. Where the risks within the water system change, as with the COVID-19 outbreak due to a change in use, the risk assessment must be reviewed and revised as necessary. This may only need to be a simple written description of the extra measures being taken at this time.
You should assess the likely timeframes and levels of occupancy against the water systems and services installed and any necessary works that need to occur prior to reoccupation.

In tenanted buildings, some floors may move back in before others and some may be
re-structuring to continue working from home longer term. Apply your approach to these areas accordingly.

Consideration should also be given to the population in your buildings as they reoccupy, as the risks may have changed. Any confirmed cases of COVID-19 within the building may mean in increased susceptibility to legionella. It is possible that cases of Legionnaires’ disease may go undetected and be confused with the similar COVID-19 symptoms, so it is even more vital that water systems are effectively managed at this time to prevent this from occurring.

Use your water management system actively to reflect the changes in activity and clearly document and record them along with any additional control measures introduced or control measures removed if no longer required.

The responsible person should continue to review the activity and records regularly in order to:

  • confirm control is being achieved and maintained;
  • identify areas where control may not be achieved so the scheme of control can be amended; and
  • monitor any further changes in occupancy (upwards or downwards) and adjust any control measures as needed.

Where water service fall under the control of a tenant they should be reminded of their ongoing responsibilities too, as well as any changes you may have made that could affect them.

Hot and cold water services

At this time, when people are starting to return to work in in their office buildings (possibly in a phased process), it is important that a suitable, dynamic flushing regime is maintained as the occupancy levels return to normal. Any Flushing should be completed weekly for a minimum of 5 minutes at infrequently used outlets, showers and spray taps.

It would be beneficial for engineers completing flushing to carry out temperature readings at all outlets, or at the very least sentinel outlets, to help identify any high risk areas they need to focus on. This will also help them verify if the water temperature is comparable with other areas of the period, and that the flush has therefore been sufficient. This will be of particular importance, given the recent warm weather, or if there has been no ongoing maintenance regime during the lockdown.

For sites where cold water tanks have been temporarily bypassed or where multiple, linked tanks or water heaters have been operating using just one vessel to reduce capacity, appropriate recommissioning will need to occur. This will likely involve a clean and chlorination of the isolated storage vessels or a pasteurisation, in the case of hot water systems, and should take into account potential biofilm build up. You should also consider, and include where necessary, smaller local heaters that may not have had regular use during this time.

You will need to confirm the availability/projected lead times of your water treatment company to complete any disinfections in line with your timescales for recommissioning the building.

It is also important to consider units that are connected to your water services, such as coffee machines, water dispensers or ice machines that may have been left operational but have not been regularly flushed. These will need to be cleaned and flushed as necessary in accordance with the manufacturer’s instructions. This may also be a good time to review and confirm your cleaning company’s cleaning procedures (where applicable) to ensure that separate cloths are used for each unit and kitchenette tap etc, so that the risks of cross contamination are minimised.

If there has not been a suitable PPM schedule in place during the lockdown period, then all other maintenance tasks such as temperature testing, shower de-scaling and tank inspections etc. should be completed as a matter of priority. This should be done, taking into consideration the additional risks posed by the water systems due to the lack of use.

As previously stated, a person who has had a confirmed case of COVID-19 could potentially have an increased susceptibility to legionella upon their return to work. This makes the ongoing shower maintenance a vital control measure.

Where any higher hazard droplet generating outlets (such as showers and spray taps, etc.) have been temporarily removed, these outlets will need to be suitably cleaned and disinfected before being brought back into use.

Additional sampling and testing of the water systems can also be employed as part of your reoccupation process to ensure control of the water systems is being achieved. This is particularly useful in buildings where, for example, the system is:

  • large and complex with a number of higher risk factors (vulnerable population, multiple spray outlets, etc.);
  • historic control indicates the system has “struggled” at times in maintaining control;
  • there are concerns relating to the water services, due to a lack of control measures and maintenance regimes in operation during the lockdown.

Legionnaires’ disease Part 2: The control of legionella bacteria in hot and cold water systems (HSG274 Part 2) states:

“Buildings temporarily taken out of use (mothballing)
2.52 The systems should be recommissioned as though they were new (i.e. thoroughly flushed, cleaned and disinfected) before returned to use."

If your building has been drained and isolated, or partially drained and isolated during the lockdown period, then a full clean and chlorination should take place prior to reoccupation. This will need to be carried out by a competent service provider, ensuring that all the relevant systems are captured, and the water is pulled through to each outlet. A suitable risk assessment for the task should also be in place.

Evaporative cooling systems (wet cooling towers)

Given the high risk nature of these systems, it is likely that a “business as usual” approach for the written scheme of management has been maintained during the lockdown period. If this has been the case, then the PPM schedule should continue to be followed and the system maintained as normal.

If there has been no requirement for cooling on site, due to it being vacant or if the cooling system has been shut down due to lack of resource for the necessary maintenance, then HSG274 Part 1 states:

“1.80 A cooling system should always be inspected, disinfected and, if required, cleaned if there is a significant change in operation status such as:

  • after any prolonged shutdown of a month or longer (a risk assessment may indicate the need for cleaning and disinfection after a period of less than one month, especially in summer and for health care premises where shutdown is for more than five days);”

The usual clean and disinfection process will need to be followed upon re-instatement. Again, check with your supplier/contractor on lead times and availability for this work.

For sites that have had gaps in the PPM schedule during this time, due to lack of resource or competent staff available, then the additional risks need to be addressed to ensure that control is regained of the system. HSG274 Part 1 states:

“1.27 The cooling system should be kept in regular use whenever possible. When a system is used intermittently, arrangements should be in place to ensure that treated water circulates through the entire system this should be monitored and records kept. The system, including the fans, should run for long enough to distribute the treated water thoroughly.

1.28 If a system is to be out of use for a week or longer, e.g. up to a month, biocides should continue to be dosed and circulated throughout the system, at least weekly. If a system is to be out of use for longer than a month it should be drained and shut down. The system, including the water treatment regime, should be recommissioned before reuse.”

If the above has not been able to be implemented, or if there is no evidence to confirm that the water has been sufficiently dosed and circulated, then a shot dose should be carried out and consideration given to a full clean and chlorination of the system based on dip slide or sample readings. This is another instance, where additional sampling may provide the reassurance that the control measures in place are adequate.

It is highly likely that there will be an increased demand for specialist work (clean and disinfection, pack inspection, etc.) during the period of time as sites begin to recommission their wet cooling systems. You will need to discuss availability for these works with your supplier and confirm a suitable, risk-based approach prior to reoccupation. You should also confirm stock levels and availability of treatment chemicals, reagents and other products (e.g. salt, dip-slides, calibration fluids etc.) and lead times on reordering as necessary.

Other water systems

All other water systems that you are responsible for should be covered in your risk assessment together with the written scheme of control to manage them.

Legionnaires’ disease: Technical guidance Part 3: The control of legionella bacteria in other risk systems (HSG274 Part3) states:

“3.6 As with all foreseeable risk systems, there is a duty to carry out a risk assessment to decide whether further actions are needed and to maintain records of all maintenance carried out, together with monitoring results. These systems and any others found to present a risk need to be adequately controlled and will often require a combination of measures, such as regular maintenance to ensure the system is kept clean, regular disinfection and ongoing monitoring where appropriate.”

For all non-essential water systems that have been drained down, such as water features, the focus should be on recommissioning the services required for critical business operation (such as domestic and wet cooling) before these systems are brought back into use.

This should be done following your normal commissioning procedures, and include a clean and chlorination of the system, where necessary.

Once reinstated, these water systems will require their normal monitoring and maintenance tasks to be completed as per the PPM schedule.

Additional considerations/information

Whilst most water related challenges resulting from the management of COVID-19 will be linked to stagnation and lack of use, these, as well as buildings that have remained operational, may have some unintended consequences of the actions you or others take during the reoccupation process. Whilst most water related challenges resulting from the management of COVID-19 will be linked to stagnation and lack of use, these, as well as buildings that have remained operational, may have some unintended consequences of the actions you or others take during the reoccupation process.


For example, you may experience higher than usual demand for hot water due to additional handwashing when buildings re-open if hygiene concerns persist. It is likely during such periods of high demand that temperatures may fall below the recommenced 50°C-60°C range. This is not uncommon during high demand, particularly if outlets are served by small volume local immersion heaters. In such cases it is important to continue with your routine temperature checks and undertake these at a period of low demand – i.e. early morning prior to building use and after heaters have recharged overnight.


Assurity Consulting will continue to take guidance from authoritative sources including Public Health England and the Government regarding COVID-19. As further information becomes available so we will update this guidance as required. Sources of information include:

1. COVID-19: General advice (GOV.UK)

https://www.gov.uk/guidance/wuhan-novel-coronavirus-information-for-the-public 

2. Legionella risks during the coronavirus outbreak (HSE)

https://www.hse.gov.uk/news/legionella-risks-during-coronavirus-outbreak.htm#:~:text=If%20your%20building%20was%20closed,the%20risks%20of%20Legionnaires’%20disease

3. Legionnaires’ disease: lockdown risks and reopening safely (CIEH) 

https://www.cieh.org/media/4208/legionella-guidance-covid-19.pdf

4. COVID-19: Advice for employers and businesses (GOV.UK) 

https://www.gov.uk/government/publications/guidance-to-employers-and-businesses-about-covid-19/guidance-for-employers-and-businesses-on-covid-19#what-to-do-if-a-member-of-staff-or-the-public-with-confirmed-covid-19-has-recently-been-in-your-workplace 

5. Coronavirus (COVID-19): latest information and advice (HSE) 

https://www.hse.gov.uk/news/coronavirus.htm

This guide was produced on the 26th March 2020 (and last updated on 25th June 2020)

For information on the services Assurity Consulting provide, please get in touch.

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