Since the identification in the late 1970s of the lung infection that came to be known as Legionnaires’ disease – the name owing to the fact that this arose from a large pneumonia outbreak among attendees of an American legion convention – it has been crucial for those responsible for a broad range of premises to be alert to the risks presented by legionella bacteria.

Legionnaires’ disease, while uncommon, can be extremely serious, and can be contracted as a result of the sufferer having breathed in tiny droplets of water in which the legionella bacteria was present.

Outbreaks of this illness can be made more likely when the bacteria are able to get into the water supply at premises such as offices, hotels, and hospitals. But if you are responsible for the control of premises like these, what do you need to know about legionella risk assessments, and the frequency with which they should be undertaken?

legionella risk assessment

What is a legionella risk assessment?

As the term suggests, a legionella risk assessment is a process by which the risk posed to certain premises by legionella bacteria is assessed.

It is a legal requirement to carry out a legionella risk assessment – or ‘LRA’ – under the Health and Safety at Work Act 1974, and it is expected that the person undertaking the assessment will be someone with the competence and authority to initiate physical and administrative checks.

What does the guidance say?

An important document of reference for duty holders – including employers – who are seeking to determine how they can meet their legal duties in relation to the legionella risk on their premises, is the Health and Safety Executive (HSE)’s Approved Code of Practice (ACOP) and guidance document, entitled Legionnaires’ disease: the control of legionella bacteria in water systems. This document was given its fourth edition (L8) in 2013.

Of particular relevance in this document are paragraphs 25 and 47, which set out that legionella risk assessments should be regularly reviewed, as well as whenever a change of circumstances occurs that could impact on the risk.

Another relevant source of guidance is section 10.1 of the British Standards Institution (BSI)’s BS8580-1:2019, which further explains the changes that might bring about a need for an existing assessment to be reviewed.

Are legionella risk assessments mandatory?

To re-emphasise what we said above, current legislation makes clear that there must be a valid legionella risk assessment in place for every commercial premises in the UK. If this is not the case for your own site, you run the risk of your premises being immediately closed, as well as prosecution and even a prison sentence in the event of a disease outbreak.

How often should a legionella risk assessment be undertaken?

The aforementioned ACOP document used to state a two-year frequency for risk assessments; however, this was removed for its fourth edition in 2013. This was partly due to the HSE’s acknowledgement that some water systems present a very low inherent risk, which means that more elaborate controls are not needed.

Today, the specific circumstances that apply to your premises will guide your efforts to determine an appropriate frequency for legionella risk assessments. Those circumstances should become clear from the risk assessment itself.

If the building for which you are responsible does not have any history of Legionnaires’ disease outbreaks or this is the first time you will be carrying out an assessment for this site, it is probably advisable to undertake an legionella risk assessment approximately every one to three years. If, on the other hand, there has been at least one outbreak within the last five years, it would be a good idea to have an legionella risk assessment carried out every year to help guard against the risk.

When you come to carry out your legionella risk assessment, it will need to encompass all aspects of your premises’ plumbing and heating, ventilation, and air conditioning (HVAC) systems, addressing potential sources of contamination within the property such as air handling units or cooling towers. In the event of these areas not having any known problems, you may safely conclude that an inspection doesn’t need to be carried out as often as once a year.

What do you need to know about water monitoring?

It is not enough to simply have legionella risk assessments carried out at your premises at an appropriate interval; you should also put arrangements in place for the continual monitoring of your building’s water systems, to help guard against the risk.

To this end, you may contact professionals who can visit your premises every month, quarter, six months, or year, providing services like microbiological water sampling. You might also train your staff in how they can effectively keep an eye on the water systems in the building.

Clinical risk assessments will be needed additional to the legionella risk assessment, considering such factors as the vulnerability of those using the premises, and the pathways by which water could come into contact with building occupants and invasive medical devices.

Who can carry out a legionella risk assessment?

As the Health and Safety Executive has previously set out, if you are an employer or another individual who is in control of the given premises, you will be required to appoint a person or persons whose responsibility it will be to help you manage your health and safety duties.

In the HSE’s words, “a competent person is someone with the necessary skills, knowledge and experience to manage health and safety, including the control measures.” This could involve you appointing yourself to the role, one or more of your workers, or someone from outside your organisation – or a combination of these.

With regard to the latter, you might choose to hire a specialist company that is registered with the Legionella Control Association.


Hopefully, the above will have provided the information and insights necessary to help you determine a suitable frequency for the legionella risk assessments that you arrange for your premises.

Did you know that specialised legionella risk management software is available to help take a lot of the stress and hassle out of the process of achieving legionella compliance for individuals and organisations like you? Furthermore, Vision Pro represents one of the best such software packages, a dedicated legionella module within this cloud-based system being easy to access, navigate, and use.

To learn more about our software platform and to arrange your demo, please don’t hesitate to call our team today.