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Frequently Asked Questions (FAQs)

HSE is only able to provide generic information on health and safety issues and cannot give specific advice on individual cases as the circumstances of each individual situation will be different, and ultimately only the courts can give an authoritative interpretation of the law when considering the application of the Health and Safety at Work Regulations (HSWA) and the Management of Health and Safety at Work Regulations (MHSWR).

You can find guidance that is more detailed on your duties in the Approved Code of Practice and guidance Legionnaires' disease: The control of legionella bacteria in water systems (L8). This contains practical guidance on how to manage and control the risks in your system. Following the guidance is not compulsory and you are free to take other action, but if you do follow the guidance you will normally be doing enough to comply with the law.

Copper ionisation systems

What is the issue over copper ionisation in legionella control?

HSE's information 29/11/2012, latest update 18/02/2014:

Latest update (18 February 2014) - Important information for users and suppliers of water treatment systems that use elemental copper for legionella control

The use of copper ionisation in legionella control

HSE submitted an application for ’essential use derogation‘ to the EC to allow for the continued use of copper in Legionella control systems within the UK, as the Biocidal Products Directive and the national Biocidal Products Regulations 2001 (which implement the Directive in Great Britain) no longer allowed the marketing and use of elemental copper as a biocide from 1 February 2013.

The Commission have, of 15 February 2014, formally granted the UK essential use derogation which allows the placing on the market of biocidal products containing copper (EC No 231-159-6; CAS No 7440-50-8) for Product Types 2 (control of Legionella in water for human use, such as bathing and showering water) and 5 (control of Legionella in drinking water). The Commission formally published their decision in the Official Journal of the European Union on 15 February 2014.

The Q&A below should help address any further questions you may have.  Alternatively, further advice about the biocidal use of elemental copper can be sought from the biocides helpdesk biocides@hse.gsi.gov.uk and about responsibilities to control the risk of exposure to legionella from COSHH.enquiries@hse.gsi.gov.uk.

For more details on the biocides directive please see HSE Biocides web site.

- Health and Safety Executive


Can I view the European Commission’s decision on the ’essential use‘ derogation application?

The UK Competent Authority for biocidal products submitted an application for an essential use derogation for the placing on the market and use of copper for biocidal product-types PT02 and 05, in accordance with article 5 of Regulation (EC) No 1451/2007. The European Commission have, of 15 February 2014, formally granted the UK essential use derogation which allows the placing on the market of biocidal products containing copper. The Commission formally published their decision in the Official Journal of the European Union on 15 February 2014.

What does an ’essential use‘ derogation mean for my system?

The favourable decision by the EC for the essential use derogation application allows for the continued use of elemental copper and the placing on the market of biocidal products containing copper whilst industry provides the data required under the Directive by a specified deadline.

What other legionella management systems are available?

HSE's guidance on the principles of legionella control and risk reduction options can be found on our legionella pages.

How can I keep up to date with progress on this issue?

For more details on the biocides directive please see HSE Biocides web site.

Appointing a competent person

Who can be appointed to test or monitor Legionella?

Anyone can be appointed as long as they have the relevant skills to implement the control measures and strategies, ie they are suitably informed, instructed, trained and assessed. They should be able to ensure that tasks are carried out in a safe, technically competent manner.

Risk assessment

Who can undertake the risk assessment for legionella?

As an employer or a person in control of premises, you must appoint someone competent to help you manage your health and safety duties, e.g. take responsibility for managing risks. A competent person is someone with the necessary skills, knowledge and experience to manage health and safety, including the control measures. You could appoint one, or a combination of:

  • yourself
  • one or more workers
  • someone from outside your business

If you decide to employ contractors to carry out your risk assessment or other work, it is still the responsibility of the competent person to ensure that the work is carried out to the required standards. Remember, before you employ a contractor, you should be satisfied that they can do the work you want to the standard that you require. There are a number of external schemes to help you with this, eg A Code of Conduct for service providers.

How do I carry out a Legionella risk assessment?

The purpose of carrying out a risk assessment is to identify any risks in your water system. The competent person should understand your water systems and any associated equipment, in order to conclude whether the system is likely to create a risk from exposure to legionella. It is important to identify whether:

  • water is stored or re-circulated as part of your system
  • the water temperature in some or all parts of the system is between 20–45 °C
  • there are sources of nutrients such as rust, sludge, scale and organic matters
  • conditions are present to encourage bacteria to multiply
  • it is possible for water droplets to be produced and, if so, whether they could be dispersed over a wide area, eg showers and aerosols from cooling towers
  • it is likely that any of your employees, residents, visitors etc are more susceptible to infection due to age, illness, a weakened immune system etc and whether they could be exposed to any contaminated water droplets

Your risk assessment should include:

  • management responsibilities, including the name of competent person and a description of your system;
  • potential sources of risk;
  • any controls in place to control risks;
  • monitoring, inspection and maintenance procedures;
  • records of the monitoring results, inspections and checks carried out;
  • a review date.

If you decide that the risks are insignificant, your assessment is complete. You need take no further action other than to review the assessment periodically in case anything changes in your system.

If I am not storing hot or cold water in my system, do I need to carry out a risk assessment?

Yes. There may be other factors within your system that increase the risks of legionellosis, eg deadlegs, shower heads and/or long runs of pipe work containing warm water. A risk assessment also considers the people who could be potentially exposed to any legionella bacteria in your system, as well as any particular groups that are at a higher risk of contracting legionellosis. However, once you have completed your risk assessment you may decide that the risks are insignificant. If you do, you need take no further action other than to review the assessment periodically in case anything changes in your system.

Controlling Legionella

How do I control the risks from legionella in my water system?

The key point is to design, maintain and operate your water services under conditions that will either prevent or adequately control the risk from legionella bacteria. It is important that you either have, or have access to, competent help to fulfil these obligations.

If you identify a risk that you are unable to prevent, you must introduce appropriate controls. You should introduce a course of action that will help you to control any risks from legionella by identifying:

  • the components of your system, eg developing a written schematic;
  • who is responsible for carrying out the assessment and managing its implementation;
  • the safe and correct operation of your system;
  • what control methods and other precautions you will be using;
  • what checks will be carried out to ensure risks are being managed and how often.

You should where appropriate:

  • ensure that the release of water spray is properly controlled;
  • avoid water temperatures and conditions that favour the growth of legionella and other micro-organisms;
  • ensure water cannot stagnate anywhere in the system by keeping pipe lengths as short as possible or by removing redundant pipe work;
  • avoid materials that encourage the growth of legionella (The Water Fittings & Materials Directory references fittings, materials, and appliances approved for use on the UK Water Supply System by the Water Regulations Advisory Scheme);
  • keep the system and the water in it clean;
  • treat water to either kill legionella (and other microorganisms) or limit their ability to grow.

What duties does the responsible person have?

The responsible person will take day-to-day responsibility for managing the control of any identified risk from legionella bacteria. They should be a manager, director, or have similar status and sufficient authority, competence and knowledge about the installation to ensure that all operational procedures are carried out in a timely and effective manner. If a dutyholder is self-employed or a member of a partnership, and is competent, they may appoint themselves. The responsible person should have a clear understanding of their duties and the overall health and safety management structure, and policy in the organisation.

Testing/monitoring Legionella

How do I test or monitor legionella from my water system?

The sampling method should be in accordance with ISO 11731:1998 and the biocide, if used, neutralised where possible. Water samples should be tested by a UKAS-accredited laboratory that takes part in the HPA External Quality Assessment Scheme for food, water and environmental microbiology. The laboratory should also apply a minimum theoretical mathematical detection limit of <= 100 legionella bacteria per litre of sample.

How often should I test water for Legionella?

It depends on the system that you have and the outcome of your risk assessment. For open systems, such as cooling towers, evaporative condensers and spa pools etc, routine testing should be carried out at least quarterly. However, there may be circumstances were more frequent sampling may be required.

For hot and cold water systems, which are generally enclosed, i.e. not open to the elements and significant contamination in the same way as cooling towers, there may be circumstances where testing for legionella is necessary. For further guidance, see Monitoring for legionella.

How do I interpret legionella test results?

Consider what the results mean in the context of your water system. Your subsequent specific actions will depend on your risk assessment. Legionnaires' disease: The control of legionella bacteria in water systems (part 2 section 128 - table 2: Action levels following microbial monitoring for cooling towers, and part 2 section 189 - table 4: Action levels following legionella sampling in hot and cold water system) contains information about what action to take when certain levels of legionella are identified in cooling tower water systems and hot and cold water systems.

Use of a water treatment company

Do I have to use a water treatment company?

No. This may not be necessary, providing you have the competence, ie knowledge and skills to fulfil your health and safety duties, eg take responsibility for managing the control scheme.

Cleaning and disinfecting water systems

Is it necessary to clean and disinfect my water system?

It is important to maintain the cleanliness of your water system. The mechanisms and frequency for doing this will depend on the system you have and whether cleaning or disinfecting is being done routinely or as a result of a problem being identified during monitoring. The frequency and method of routine cleaning and disinfecting should be identified within your risk assessment. This will take account of factors such as whether the system is open or closed, the type and level of contamination, and the population that could be exposed.

As a landlord, what are my duties?

Organisations, or self-employed individuals, who provide residential accommodation or who are responsible for the water system(s) in their premises, are responsible for ensuring that the risk of exposure to legionella in those premises is properly controlled.

This means that they have a duty to assess the risk from exposure to legionella to their staff, residents, guests, tenants and customers by implementing appropriate control measures. This is especially important in residential buildings, where vulnerable people may be at risk, such as retirement flats, or where the accommodation is provided specifically for a group who may be susceptible to legionelloses.

Specific risk systems

Cooling towers

I can't get the pack out, how do I show it is clean?

It will be necessary for you to show that the pack is clean. There are a number of ways you can approach this and you may also wish to consider the information in Removal of pack from cooling towers.  

Hot and cold water systems

How often do I have to check the temperature of my system?

That depends on the outcome of your risk assessment and the components of your system. For hot and cold water systems, advice is available in the Hot and cold water table

In my care home I have a number of Thermostatic Mixing Valves, what are the key issues?

TMVs are an important mechanism to prevent scalding in health and social care settings where, for a number of reasons, there are increased water temperatures. A TMV will reduce the water temperature at the outlets to prevent scalding. More information can be found on the Scalding and burning website.

The reduction in the temperature of the outlet has the potential to increase risks of legionella bacteria growth. In order to manage this risk, the TMVs should be sited as close as possible to the point of use and flushed regularly. Further information about monitoring the temperature of the water at a TMV can be found in the Hot and cold water table.

Spa pools

I have a spa pool – is there a risk from Legionellosis?

Spa pools are a significant risk of legionellosis if they are not maintained adequately. You can find guidance that is more detailed on your duties in Management of Spa Pools - Controlling the Risks of Infection

Other risk systems

How do I know if I am operating a water system that may be a risk from legionellosis?

To identify the sources of risk in your water system, you must under take a risk assessment. The competent person, should understand your water systems and any associated equipment. If you understand your water system, you will be able to establish whether it is at risk of exposure to legionella. Identify whether:

  • water is stored or re-circulated as part of your system
  • the water temperature in some or all parts of the system is between 20–45 °C
  • there are sources of nutrients such as rust, sludge, scale and organic matters
  • conditions are present to encourage bacteria to multiply
  • it is possible for water droplets to be produced and, if so, whether they could be dispersed over a wide area, e.g. showers and aerosols from cooling towers
  • it is likely that any of your employees, residents, visitors etc are more susceptible to infection due to age, illness, weakened immune system etc and whether they could be exposed to any contaminated water droplets

If you decide that the risks are insignificant, your assessment is complete. You need take no further action other than to review the assessment periodically in case anything changes in your system.

Updated: 2014-06-10