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Why water management is vital to prevent legionnaires disease

By: Jon Greaves on Jan 19, 2022

Legionnaires’ disease is a severe and potentially fatal type of pneumonia resulting from infection. People contract the disease by inhaling droplets of water containing a bacterium known as legionella, which can be found in most water sources. However, in constructed water systems, including spa pools, air conditioning units, humidifiers, cooling towers, and hot and cold water systems, favourable conditions allow bacteria to grow and be sent out as an aerosol providing a route to infection. 

Legionnaires’ disease can be present in all water systems; however, it is mainly brought to the public’s attention when it is caught in offices, hospitals, hotels, and care homes where bacteria have managed to enter the water supply and been aerosolised. Fortunately, there is a relatively simple answer—efficient water management will inhibit bacteria from growing, help comply with the legislation and guidance, and potentially save lives.

What legislation applies to Legionella?

The Health and Safety at Work etc Act 1974 (HSWA) describes duties that may arise from work activities, encompassing risks from legionella bacteria.

The Management of Health and Safety at Work Regulations 1999 (MHSWR) provides a broad framework for controlling health and safety at work.  

The Control of Substances Hazardous to Health Regulations 2002 (COSHH) provides a framework of actions designed to assess, prevent, or control the risk from bacteria such as Legionella and to help take suitable precautions.  

More specifically, the Approved Code of Practice: Legionnaires Disease (ACoP L8) provides practical advice on managing and controlling risks associated with Legionella. It is aimed at employers, those in control of premises, and those with health and safety responsibilities for others. Its purpose is to help duty-holders comply with their obligations concerning legionella, including: 

  • Identifying and assessing sources of risk 
  • Preparing a scheme to prevent or control risk
  • Implementing, managing, and monitoring precautions
  • Keeping records of precautions
  • Appointing a manager to be responsible for others

ACoP L8 also provides practical advice for duty-holders to actively manage and control Legionella risk in their environment, including:

  • Ensuring the proper control of aerosol release 
  • Avoiding water temperatures or conditions that support the growth of Legionella
  • Eliminating the use of any materials that may encourage the growth of Legionella
  • Treating water to limit the growth of Legionella
  • Keeping pipe lengths short to avoid stagnation of water 
  • Maintaining records of control measures, repairs, and maintenance

What are my obligations as a duty-holder?

  • Conduct a Legionella Risk Assessment: a formal assessment of on-site assets checking for all potential sources of Legionella risk, including water storage system condition, system hygiene, temperature checks, and legionella control measures. This should be carried out in accordance with BS 8580:2010

  • Write a Scheme of Control for Legionella: a comprehensive risk management document that identifies measures required to control the risks from exposure to Legionella bacteria. It should also detail how the measures are implemented and managed to control water systems effectively. You should keep a hard copy of this document.

  • Appoint a ‘competent person’: someone with sufficient authority and knowledge of the institution to help take the measures needed to comply with the law.
  • Keep records of every action taken that is part of your legionella control programme, including monitoring, inspections, and maintenance. Additionally, you must keep a record of every established management process, including copies of your risk assessment and when the recommendations have been adhered to. All records need to be easily accessible for auditing. Most records must be kept for two years, but the results of monitoring inspections, checks, or tests must be kept for five years. Records will typically contain information, including the following:

    • Staff training
    • Information on the system and how it operates
    • Material Safety Data Sheet (MSDS) information
    • Audits of the Legionella control programme
    • Chemical and microbiological analysis reports and certificates
    • A list of control parameters
    • Defect and fault management records for results outside of control parameters
    • Planned Preventative Maintenance (PPM) programme

  • Comply with your additional duties as the duty-holder, including: 

What is good water management for legionella? 

The key to managing legionella bacteria lies in temperature control. Legionella bacteria can only multiply in water where temperatures range between 20–45°C due to the nutrients available at this temperature. Below 20°C, legionella survives but is dormant, and above 60°C, most bacteria cannot survive. Therefore, water management to prevent legionella means operating constructed water systems at temperatures that prevent Legionella growth.

Using temperature control to control legionella (Please note there is separate guidance exists for Clinical Settings) 

  • Store water in hot water storage cylinders (calorifiers) at a minimum temperature of 60°C 
  • Distribute hot water at a minimum temperature of 50°C
  • Store and distribute cold water at a maximum temperature of 20°C
  • A competent person should routinely check distribution temperatures in the furthest and closest outlets to each tank or cylinder in the system (every month for hot water tanks and biannually forcold water tanks).

Additional controls for legionella 

In addition to temperature controls, there are several other things to look out for as part of a sound water management system.

Stagnant water: Stagnant water favours Legionella growth. Seldom used showerheads and taps should be flushed weekly and de-scaled quarterly. Hot water tanks should be drained regularly to inspect for debris, and cold water tanks should be inspected and then cleaned on a risk assessment basis.

Biocide treatments: Biocides are compounds that can kill microbes and can be key to controlling risks in problematic legionella-susceptible systems. They are commonly used in the water treatment system of cooling towers and in the domestic water supply system to control legionella bacteria.

Water samples: Water samples should be taken and analysed (as described in your risk assessment) for the presence of legionella bacteria to confirm that counts are acceptable. 

Extra methods: 

  • Use materials that do not encourage the growth of Legionella bacteria
  • Insulate pipes and tanks
  • Prevent contamination by using lids
  • Make sure pipes are as short and direct as possible

Checklist to ensure good water treatment management

Here are eight key questions to ensure you have a good water treatment programme:

  1. At what temperature is the water being stored? Remember, legionella bacteria grow at temperatures between 20–45°C.
  2. Is the System clean and inspected regularly?
  3. Is there any corrosion in the water system pipes? Corrosion can facilitate legionella bacteria growth, depending on several water quality variables, including disinfectants used, pH levels, and water temperature.
  4. How long has the water remained in the system? The longer water remains in a system, the more likely it is that pathogens can grow. 
  5. Are there any cross-connections? Cross connections between potable and non-potable water can introduce Legionella into the potable water supply.
  6. Are there any dead legs? A ‘dead leg’ is a pipe leading to an outlet through which water flows, but the outlet is rarely used or unused.
  7. Has a biofilm formed on the inside wall of the water supply piping? Biofilm protects Legionella from heat and disinfectant, meaning conditions are more suitable for the bacterium to grow.
  8. If a biocide is being dosed, is it operational, and are correct levels being distributed through the system?


Legionnaire bacteria are invisible and a potential killer. Therefore, each building must appoint a duty-holder whose job it is to comply with the regulations. This includes carrying out a Legionella Risk Assessment, writing a Scheme of Control for Legionella, and keeping records of the building’s Legionella programme. 

The duty-holder must establish a programme for efficient water management, which addresses the dangers of legionella by preventing bacteria from growing, helping comply with the legislation, and saving lives.

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Topics: Legionella Control

Jon Greaves

Written by Jon Greaves

Jon has progressively worked through operational roles, account management, technical management, and senior management roles over the last 16 years within one of the group companies before moving into the role of Water and Air Managing Director. Jon has experience across multiple sectors of water and air compliance, including district energy networks; data centres; healthcare; food and beverage and facilities management. Jon acted as a corresponding steering committee member on CIBSE CP1 – Heat Networks Code of Practice for the UK released in 2020.

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