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How to mitigate Legionella outbreaks in cooling towers of large buildings?



Maybe you have heard about legionella bacteria, Legionnaires disease, or Legionellosis but you are not entirely sure of the risks involved when it comes to the water systems of your building. An individual infected with this disease may develop a very serious pneumonia which can be lethal in some cases. According to recent studies, only in developed countries there are thousands of ourbreaks every year in which 10 per cent of people actually dies. Also, in 90 per cent of the cases, these outbreaks were perfectly preventable.

In an attempt to aid building managers and owners with handling cooling towers, we are sharing five aspects to consider when it comes to the assistance of mitigating legionella outbreaks in water systems of large buildings.


What exactly is Legionnaire disease?

There are more than twenty five related species of Legionella bacteria in nature. They are naturally present in rivers, streams and lakes and are relatively harmless. The bacteria group responsible for Legionella illness, and the most lethal one, is Legionella pneumophila. It actually becomes a real health concern when it can be found in our water systems.


Why is it a health issue in our water systems and not in nature?

Once the bacteria species becomes airborne, evaporation of water in cooling towers, it has the capability to move through air currents and therefore infect people near the source of contamination. After the infection has happened, a pneumonia can be developed.


Who is at risk?

All building managers and owners with cooling towers or even with evaporative condensers for their spas/whirlpools, misters, ornamental fountains and humidifiers are at risk.


Is there anything we can do to mitigate these risks?

Yes, here are five aspects to consider when it comes to mitigating the risks:


  1. Evaluation of the water system: does the building have one or more of the items listed earlier as a risk factor (misters, cooling towers, fountains, etc.)?
  • Identify potable water systems
  • Location of the systems
  • How the water is processed and received
  • Identify potential risks with the systems water flow – process flow diagram


  1. Water treatment program
  • Get a water treatment professional to put in place a water treatment program: Recurring water treatment is needed. Bear in mind that several high performing water disinfection tools are available to avoid recurring and expensive chemical cost.
  • Guarantee there is no stagnation of water – Legionella grows in warm waters between 22 to 40 degrees. Guarantee that there are no dead-arms in the water system and make sure there is an adequate water recirculation.
  • Make sure that the plan includes a contingency plan in case of outbreak.
  • Control and communication: make sure you share the plan with the team and assign clear responsibility of tasks.



  1. Limit the spread of mist
  • Various solutions available on the market can assist in decreasing the mist spray from travelling from the water systems.


  1. Monitor and control
  • Monitor locations in key areas
  • Establish a schedule to take samples: there are several easy-to-use tools to monitor the bacteria amounts in water. Make sure to include a Legionella testing every month of operation.
  • Run a legionella risk assessment regularly.


  1. Request help
  • There are several water consultants you can get in touch with in order to assist you. They can develop a plan adapted to your building water system.

Utilising temperature control

The main method utilised to monitor and control the risk from Legionnaires disease is indeed water temperature control.

Water services must be operated at temperatures that will prevent Legionella growth:

  • Hot water storage cylinders needs to store water at 60°C or more
  • Hot water must be distributed at 50°C or more (thermostatic mixer valves have to be fitted as close as realistically possible to outlets, where a scald risk is in fact identified).
  • Cold water must be stored and distributed below 20°C.

A competent person should routinely have a look, check, inspect and clean the system, in accordance with regulations of the risk assessment.

You need to identify ‘sentinel’ outlets (closest and furthest to each cylinder or tank) for monthly checking of the distribution temperatures. You need to also check the water storage cylinder temperatures every month at least once and cold water tank temperatures once at least every 6 months.

Stagnant water does favour Legionella growth. To reduce the risk you need to remove dead legs/dead ends in pipes, flush out rarely used outlets (including taps and showerheads) at least once per week and clean and de-scale shower heads as well as hoses at least quarterly. Cold-water storage tanks need to be cleaned regularly and water must be drained from hot water cylinders to check for potential debris or signs of corrosion.

Design systems to reduce or minimise Legionella growth, by:

  • keeping pipes as short and direct as realistically possible;
  • adequately insulating pipe-work as well as tanks;
  • utilising materials that don’t encourage the growth of Legionella bacteria;
  • preventing and avoiding contamination, eg by fitting tanks with lids as well as insect screens.

Additional monitoring controls

Water samples must be analysed for Legionella bacteria periodically in order to demonstrate that bacteria counts are acceptable and low enough. The frequency needs to be determined by level of risk, and of course in accordance with the risk assessment.


Other monitoring control systems

Other monitoring methods to control Legionella bacteria growth include silver and copper ionisation as well as biocide treatments (like chlorine dioxide). To guarantee that they remain efficient their application will require suitable assessment as part of the general water treatment program including an adequate installation, maintenance as well as monitoring.


How the Kimberley Process Is Making A Difference in Global Diamond Trade



Unethical and unlawful practices have plagued the global diamond industry for many years. The Kimberley Process is a critical mechanism to help protect the integrity of the diamond supply chain and ensure that consumers worldwide can have confidence that the diamonds they purchase are conflict-free. By working together, governments, civil society, and the diamond industry have made a real difference in the global diamond trade. The Kimberley Process has provided a robust framework to prevent, detect, and combat the illegal trade of diamonds. This process has helped prevent the exploitation of diamond-rich countries and the funding of armed conflicts. The Kimberley Process has been instrumental in transforming the diamond trade and improving people’s lives in diamond-producing countries.

The Kimberley Process Certification Scheme

The Kimberley Process Certification Scheme is a system for tracking and controlling the trade of rough diamonds to ensure that the lab grown diamonds are from non-conflict areas and are not financing violent armed groups. The KP has helped combat the illegal mining of conflict minerals. In 2017, the KP transitioned from an inspection and certification regime to a certification-only regime. Under the new system, countries that produce and export rough diamonds have agreed to implement a third-party audit system to ensure full compliance with the KP’s requirements.

Benefits and Challenges of the Kimberley Process

The KP has helped transform the global diamond industry. For example, it has helped improve the lives of people living in diamond-producing countries. Diamond producers have also been able to boost their economies and generate more revenue by participating in the KP. The KP has also made it easier for consumers to purchase diamonds. Since the implementation of the KP, it has become easier for people to be assured that the diamonds they purchase are conflict-free and that their purchases are helping to reduce poverty in diamond-producing countries. The KP has also helped transform business practices in the diamond industry. For example, the KP has helped spark innovation and growth in the diamond-testing industry. The KP has also helped spark innovation and growth in technologies that track diamonds from the mine to the retailer. Consumers can also use a smartphone app to trace diamonds to their source.

Impact of the Kimberley Process

The KP has had a major impact on the global diamond trade. For example, diamonds are now synonymous with ethical practices, and the KP is recognized as a robust mechanism that helps protect the integrity of the diamond supply chain. As a result, many retailers and manufacturers have adopted the KP standards and gained assurance that their diamonds are ethically sourced. Consumers can track diamonds’ sources using a smartphone app or handheld scanner. They can also be assured that their purchases are conflict-free and help people in diamond-producing countries. Their retailer’s assurance that the diamonds are KP-compliant helps with that.


The Kimberley Process is an international effort to fight the conflict diamond trade. The KP has helped protect the integrity of the diamond supply chain and ensure consumers can be confident in their purchases.

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