Legionella, how to control and prevent.

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This can be prevented by a good layout of the water circuit. But more than often this was not sufficiently taken into account in the building process. So a good Legionella Management plan is necessary to safeguard your buildings.

As disturbing as it might sound, there are a lot of microorganisms (bacteriaarchaeafungiprotists and viruses)  living on or within human tissues and biofluids, including skin, placenta, saliva, conjunctiva, etc. Actually, we would had not made it this far in evolution without bacteria[1]. They are in our stomach, helping us to break down food to get more nutrients out of it, we have developed a strong immune system because bacteria has been there to strengthen it[1].

As beneficial as the presence of “good bacteria” in our body is, there is the counterpart, “pathogenic bacteria”, responsible for causing diseases. These begin when pathogenic bacteria enters the body and starts reproducing and outnumbering good bacteria[2].

What is Legionella and what are the effects of Legionella to our health?

Amongst pathogenic bacteria, Legionella pneumophila shows up. Legionella is commonly found in fresh water environments, like lakes or rivers, where generally is present in low amounts that do not lead to disease[3]. Once it enters building water systems, where the temperature conditions are between 20 – 45 ºC[4], it starts to dangerously replicate and spread in water droplets that people can breathe[3].

Legionella grows in pipes and many other parts of building water systems, such as hot and cold storage, heaters, expansion tanks, filters, faucets, showerheads and hoses, humidifiers, hot tubs, decorative fountains, cooling towers, etc[3].

The inhalation of contaminated water droplets lead to the legionnaire disease, which is a fatal type of pneumonia[5]. Although everybody is sensitive to catching it, the elderly, smokers, alcoholics, cancer and diabetes patients, or those with respiratory or kidney disease are more prone to get Legionnaires[5]. This bacteria is also responsible for causing the Pontiac fever and extra pulmonary syndromes, originated when the bacteria spreads to other organs[6].

Efficiency of prevention and control techniques for Legionella

Legionella can be kept at no harmful levels by water temperature control or the application of residual effects disinfectants. The fact that the bacteria are dormant below 20 ºC and do not survive above 60 ºC[5], makes temperature control a primary method. Keeping hot water storage cylinders at 60 ºC or higher, distributing hot water at 50 ºC, or higher, and cold water below 20 ºC are some used techniques[5]. Flushing with hot water (50 ºC – 60 ºC) is also another temperature control method, but it is only applicable to hot water systems[7].

Temperature control techniques are fairly simple, but they present some limitations. Keeping temperature below 20 ºC is only applicable to drinking water systems, and above 50 ºC it does not ensure to completely eliminate legionella. Moreover, hot water circulation temperature must be near 60 ºC, and although easily monitored, it is difficult to maintain such temperature range in old systems[7].

Residual effect biocides is also another legionella mechanism of prevention and control. These disinfectants, are added to the water to limit bacterial growth. Monochloramine, is an effective disinfectant against legionella, even more effective than chlorine[6]. However, it is necessary to ensure that biocides amounts in the system are high enough as to achieve the intended task, otherwise bacteria would still proliferate in the medium if adequate actions are not taken to stop it.

Disinfectants like monochloramine and chlorine show some disadvantages. They affect rubber components, are toxic to fish, and there are no commercial kits available for small water systems dosing[7]. Chlorine also presents the formation of chlorite as disadvantage, and just like monochloramine, needs a carbon filter protection for dialysis patients[7].

Legislation – employability Legionella control techniques

In Europe, efforts to combat Legionella center on public health issues. Although EU has issued a series of directives on the quality of drinking and bathing water, as well as indoor air quality, Legionella is not always mentioned in these directives[8].

At a national level, almost all European countries have adopted public health policies against legionella, whereas a few of them mention it as a special issue in their OSH (Occupational Safety and Health) legislation. In the majority of these cases, risk assessment is promoted by other documents like technical rules, guidance, codes, etc., containing technical protocols for the maintenance of cooling towers, spas or water supply systems. In some countries, these protocols are under the form of standards, whereas in others they are part of publications from responsible authorities, organizations in the cooling industry, trade unions, municipalities, etc.[8]

Belgian regulation regarding Legionella falls under the European regulation. When selecting a biocide for Legionella prevention, the user is always obliged to choose the one that is least harmful to humans and the environment. The classification of biocidal substances by harmfulness is classified according to European regulation 1272/2008 and is characterized by the well-known GHS-symbol.

A lot of this can be prevented by a good layout of the water circuit. But more than often this was not sufficiently taken into account in the building process. So a good Legionella Management plan is necessary to safeguard your buildings. 

Our experts are here to advice.


[1]          M. Ashford, L. L. M. C. | August 12, and 2010 02:18pm ET, ‘Could Humans Live Without Bacteria?’, Live Science. [Online]. Available: https://www.livescience.com/32761-good-bacteria-boost-immune-system.html. [Accessed: 21-Nov-2018].

[2]          ‘Bacterial Diseases – Bacterial Infection – Symptoms, Causes, Treatments, Diagnosis’, 26-Jun-2014. [Online]. Available: https://www.healthgrades.com/conditions/bacterial-diseases. [Accessed: 21-Nov-2018].

[3]          ‘Legionella Growth and Spread | Healthcare Facilities | CDC’, 30-Apr-2018. [Online]. Available: https://www.cdc.gov/legionella/wmp/overview/growth-and-spread.html. [Accessed: 21-Nov-2018].

[4]          ‘Temperature Effects on Legionella Proliferation in Water Systems’, Water Environmental Treatment Ltd, 24-Jul-2014. [Online]. Available: http://www.wet-services.com/blog/temperature-effects-legionella-proliferation-water-systems/. [Accessed: 21-Nov-2018].

[5]          ‘Managing legionella in hot and cold water systems’. [Online]. Available: http://www.hse.gov.uk/healthservices/legionella.htm. [Accessed: 21-Nov-2018].

[6]          J. Bartram, Ed., Legionella and the prevention of legionellosis. Geneva: World Health Organization, 2007.

[7]          D. J. Kung’u, ‘Methods to Control Legionella Growth In Water Systems’. .

[8]          ‘European technical guidelines for the prevention, control and investigation of infections caused by Legionella species’, European Centre for Disease Prevention and Control. [Online]. Available: http://ecdc.europa.eu/en/publications-data/european-technical-guidelines-prevention-control-and-investigation-infections. [Accessed: 21-Nov-2018].

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Jacob Bossaer

Founder & CEO

Jacob is the founder and CEO of BOSAQ. He has founded BOSAQ and Water Heroes to provide a sustainable water solution to the world, right after coming back from one of the most extreme places on earth.

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