Please find below a list of answers to questions our clients frequently ask us about Legionella risk assessments and water safety. If you have any further questions, please fill out our form here to arrange a free consultation with one of our experts. 


What are the most common waterborne pathogens and bacteria?

There are estimated to be trillions of trillions of bacteria worldwide!  Many bacteria thrive in moist or wet environments, along with a range of other microorganisms and some of them can be harmful to us. The huge variety of organisms means it’s not practical to check for all the potentially pathogenic organisms in our water systems all of the time. That said, there are key indicator organisms that organisations are required to proactively monitor and manage.  The Water Supply [Water Quality] Regulations apply to companies that supply water to consumers and Schedules 1 and 2 of the Regulations contain maximum permissible concentrations for these indicator organisms.  The schedules detail:

The Health & Safety Executive [HSE] provides specific guidance on how to manage the risk from Legionella bacteria in the Approved Code of Practice [ACOP] L8.  Further guidance on managing both Legionella bacteria and Pseudomonas aeruginosa within healthcare premises may be found in the Department of Health’s HTM04-01: Safe Water in Healthcare Premises: Parts A, B & C.

I have a positive Legionella count - what should I do?

In the first instance, it is important to understand the reason for taking the sample.  In the section on 'Microbiological Monitoring, the HSE's Technical Guidance HSG274 Part 2 indicates the circumstances in which sampling for Legionella is appropriate.  Sampling should be a defined strategy and not a fishing exercise.

Secondly, the magnitude of the result, i.e the number of Legionella bacteria recovered from the sample will determine the action to be taken. HSG274 Part 2, Table 2.2 details the action levels following Legionella sampling in hot and cold-water systems.

For healthcare organisations there is additional guidance on what actions to take, this can be found in HTM04-01 Part B, Chapter 10, Figure 4 - Legionella sampling in hot and cold water systems.  This later guidance provides specific help on pre and post-flush samples for an expanded range of possible results.

Each organisation should have a written scheme of control [water safety plan] that details the action to take, these can be based on the published guidance.

What are the consequences of Legionella?

Legionella is a bacterium that is common in natural water sources and, can also be found in man-made water systems within the built environment.  Such systems include cooling towers, evaporative condensers, spa pools and hot and cold water systems [to name a few].  Exposure to Legionella bacteria that have been allowed to multiply within a building water system can cause illness.  The collective name for illnesses caused by Legionella bacteria is ‘legionellosis’; the most serious form being Legionnaires’ disease. The risk of contracting Legionnaires’ disease increases with age [>50 years], heavy smoking, heavy drinking, underlying health conditions or an impaired immune system. New born babies are also at increased risk and data analysis shows that the disease affects three times more males than females.  Public Health England monitor reported cases of Legionnaires' disease and publish monthly reports; in 2018 there were 814 reported /notified cases

There is an average mortality rate of 15% but even survivors can be left severely affected as a result of Legionnaires' disease.

How can we control Legionella in our industry?

All organisations have a duty to manage the risk from health hazards, including the risk from Legionella, as required under Health & Safety at Work etc. Act 1974. Under the Control of Substances Hazardous to Health [COSHH] Regulations there is requirement to undertake risk assessments.  The HSE have published guidance in the form of ACOP L8 which is supported by the Technical Guidance HSG274 Part 1, 2 & 3.  These provide proactive and meaningful guidance on the necessary measures to manage and control Legionella.  Where the susceptibility of those who may be exposed is increased e.g.  care establishments and health care providers then additional guidance is available in the form of HTM04-01 Parts A, B & C.

Who should be involved in conducting Legionella risk assessments?

A Legionella risk assessment must be a suitable and sufficient assessment that identifies and evaluates the risk of exposure to Legionella bacteria from work activities and water systems on the premises, including any precautionary measures needed. Those persons who complete the risk assessment and provide advice on prevention and control measures must be competent to do so [as detailed in ACOP L8 Paragraph 29].  The risk assessor should be able to demonstrate experience of completing Legionella risk assessments and the precautionary measures, this maybe in the form of CV, training records and statement of qualification detailing the number of risk assessments completed. The Responsible Person [Water] and / or Authorised Person [Water] should request evidence of competence and experience and seek an interview with the risk assessor before commissioning the risk assessment. 


Others involved in conducting the Legionella risk assessment should include those who have knowledge of the building and water systems being assessed. This will include the Responsible Person [Water] and/or Authorised Person [Water] being available for interviews with the risk assessor as part of the process. They will also be able to facilitate the provision of information to aid the risk assessor [e.g. written scheme, monitoring records, previous risk assessments, schematics and risk minimisation schemes]. A competent person should also be available to assist the risk assessor with the building survey & inspection of water systems; they should know the building and be able to provide ‘insider’ knowledge. This level of input will assist the risk assessor with their final risk assessment report.

How often should I complete a Legionella risk assessment?

A risk assessment report is a living document that must be kept under review to ensure it does not become out of date.  The 2-year frequency for review of risk assessment is no longer applicable. As such those who have responsibility for actioning the risk assessment and the minimisation scheme need to routinely review the risk assessment. The frequency of reviewing is dependent on your organisation and the level of risk, for example an update on the status of the risk assessment and risk minimisation scheme maybe reported to the Water Safety Group.


The HSE ACOP L8 [Paragraph 47] provides an indication of when a review of the risk assessment, i.e. when it is time to revisit the actual risk assessment process for a building or system:


(a) changes to the water system or its use;

(b) changes to the use of the building in which the water system is installed;

(c) the availability of new information about risks or control measures;

(d) the results of checks indicating that control measures are no longer effective;

(e) changes to key personnel;

(f) a case of Legionnaires’ disease/legionellosis associated with the system.


We have previously published a blog asking  How often should a risk assessment be completed?

How do we know if we are at risk?

The risk can be defined as “the risk of exposing individuals to Legionella bacteria”. If your building has a water supply and processes associated with the water then you have a risk that needs to be assessed. The HSE ACOP L8[Paragraph  2] details there is a reasonably foreseeable Legionella risk in your water systems if:


  • water is stored or re-circulated as part of your system;
  • the water temperature in all or some part of the system may be between 20–45 °C;
  • there are deposits that can support bacterial growth, such as rust, sludge, scale and organic matter;
  • it is possible for water droplets to be produced and, if so, if they can be dispersed;
  • it is likely that any of your employees, contractors, visitors etc could be exposed to any contaminated water droplets.


It is a requirement of the COSHH Regulations and HSE ACOP L8 to assess the risk.

Why is water temperature monitoring important?

Legionella is a bacterium that is common in natural water sources and can also be found in man-made water systems within the built environment. Such systems include cooling towers, evaporative condensers, spa pools and hot and cold water systems [to name a few]. It is a requirement of the COSHH Regulations and the HSE’s ACOP L8 for the Responsible Person [Water] to implement control measures to manage the risk.  The control measures need to be monitored to prove they are being effective. The HSE recognise the use of water temperature to be a common and effective control strategy when applied correctly and consistently. Duty holders should be able to demonstrate that they have done everything reasonably practicable to control the risk and it is therefore necessary to ensure temperatures are set and maintained at the correct level by monitoring them regularly. A lapse or absence in monitoring records is a non-retrievable situation, i.e. if records lapse or are incomplete you will subsequently be unable to prove the status of the system at the time the records were missed.

How should we record reviews and assessments of our water hygiene?

Formal records are required under COSHH and HSE ACOP L8. Any review of records or assessment need to be recorded to document what has actually been reviewed, by whom and when, including any resulting actions. A formal review process of assessments should be established and followed.

What is a water safety plan (WSP) and how do we create one

The HSE's Technical Guidance HSG274 Part 2, Appendix 2.2, defines a ‘written scheme of control’ that should take the risk identified and valuated in the risk assessment, define the particular control strategy and detail the correct and safe operation of the water systems. 


The term  Water Safety Plan or WSP is taken from the Department of Health's guidance HTM04-01 Parts A, B & C and is a term used for healthcare organisations when it comes to the written scheme of control. 


The WSP is a risk management approach to the safety of water within an organisation. The WSP will outline:

  • good practices for storage, distribution and supply of water;
  • identify potential hazards;
  • detail control measures required.


Before a WSP can be fully developed, a risk assessment is needed to identify all the associated water risk systems and to enable this information to be captured within the scope of the WSP. The WSP won’t necessarily be one document, it can be made of several documents with distinct purposes, e.g. the risk assessment element identifies the associated water risk systems, the standard operating procedures [SOPs] describe the correct and safe operation of the systems and the emergency action plans [EAPs] will provide the necessary information and protocols to guide an organisation through water-related safety incidents.

How can we manage our little used outlets?

Little used outlets [LUO], as the name suggests, are those outlets that are not routinely used or that are not used at all. This lack of use can be due to a number of reasons, such as a change of use in a room / area, an outlet that is no longer required or an outlet that is broken.


The key element to the management of LUOs is knowledge of their existence. As such, awareness of what a LUO is and the risks created from them need to be shared with individuals who interact with outlets i.e. Competent Persons, Cleaners / Domestics, Building Managers etc. Their feedback on whether LUOs exist will help on the correct course of management. Those actions can include:

  • where an outlet is no longer needed – remove and cut back all associated pipework to the main distribution runs;

  • where an outlet can’t be removed - establish a flushing program. The frequency and duration of flushing needs to be assessed to determine the correct method for individuals to follow.

What is a Water Safety Group?

The management of water safety doesn’t necessarily fall to one person! The proactive management of water safety within an organisation will invariably rely on the combined efforts of several individuals who will collectively form the Water Safety Group [WSG]. The WSG:

  • is a multidisciplinary group that undertakes the commissioning and development of the WSP;
  • shall provide advice on remedial action required when water systems and outlets are found to be non-compliant or contaminated.

What is an Authorising Engineer [Water]?

Often abbreviated to AE [W]. The AE [W] is a specialist professional advisor, who should remain independent of the organisation.  The AE [W] will be a member of the WSG, will act as an advisor, monitor the performance of water safety within the organisation, undertake an annual audit and act as an assessor of competency for the appointment of those involved in water safety i.e. Responsible Person [Water] / Deputy Responsible Person [Water] / Authorised Person [Water]. The AE [W] should be formally appointed in writing by the organisation.

Who should be responsible for water safety in my organisation?

The dutyholder for the organisation has overall responsibility for management of health & safety risks within an organisation. Water safety is an element of health & safety.  The dutyholder should specifically appoint a Responsible Person [Water] [RP[W]] to take day to day responsibility for the control and management of water safety risk within the organisation. The HSE ACOP L8 [Paragraph 48], states that the RP[W] should have sufficient authority, competence and knowledge of the installation, to ensure that all the operational procedures are carried out in a timely and effective way.  The RP[W] also should have such ability, experience, instruction, information, training and resources to enable them to carry out their tasks competently and safely - it is good practice, therefore, for this person to have their competency independently assessed, for example by and Authorising Engineer [Water].

What training is important for the responsible person for water safety in my organisation?

One of the key requirements of COSHH and the HSE ACOP L8 is the provision of suitable instruction, information and training.  Investigations have shown that outbreaks of Legionnaires’ disease can be attributed, at least in part, to inadequate management, poor communications and a lack of training. The training provided must be appropriate for those being trained

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