Water Treatments – Legionella and Its Effect

Legionella bacteria are found at the air-water interface in surface water, in ground water and in aerated biofilms. Very low numbers of Legionella enter buildings and mechanical equipment in the water supply. Legionella subsequently may multiply to high numbers in cooling towers; evaporate condensers, air washers, humidifiers, hot water heaters, spas, fountains, car wash facilities, and plumbing fixtures. Water testing laboratories have carried out experiments that Legionella bacteria can increase at the rate from less than 10 per milliliter to over 10,000 per milliliter of water sample within one month.

How is Legionella spread?

Legionella infects a person when they inhale aerosols (small particles that do not settle out of the air) containing these bacteria. Legionella dispersal can extend over a distance of at least 6 kilometers. These bacteria are regularly found to be responsible for severe, sometimes fatal, human pneumopathy epidemics. Any individual can be contaminated and legionellosis is particularly severe in at risk legionella besmetting  subjects. Legionella are widespread in the environment i.e. surface waters, lakes, waterways and the bacterial reserves are essentially water-based.. They are also found in drinking water distribution systems i.e. hot water for sanitary purposes, cooling towers and establishments receiving the public hotels, campsites, etc. Legionella does not spread from person to person.

Causes of the disease

Legionella species of bacteria cause Legionnaires ‘disease. They are gram negative (but stain poorly), strictly aerobic rods. Optimal development conditions for legionellosis combine soft water with a temperature of 35-40° C. Contamination is essentially through inhalation of aerosolized organisms.


In addition, risk prevention involves regular monitoring for Legionella in water in all its forms in industrial environment, hospital environment, natural ecosystems, and artificial water networks.
Legionella have an intracellular development in protozoa such as amebas and in biofilms, which makes them very resistant.

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