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The Legionella Pneumophila bacterium thrives in water supply systems and air conditioning systems - and may cause the Legionnairs disease.

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Legionnaires disease is an acute respiratory infection caused by the Legionella pneumophila bacteria which may cause a broad spectrum of diseases - from mild cough and fever to serious pneumonia.

The bacteria thrives in temperatures ranging 69 oF (20.5 oC) to 122 oF (50 oC) and can be traced in water supply systems, central heating systems and air conditioning systems.

Note! Any water system with an operating temperature between 69 oF (20.5 oC) and 122 oF (50 oC) is a potential legionella source. Special attention should be taken for

  • cooling towers and evaporative condensers
  • scrubber systems with low temperatures
  • low temperature hot water supply systems

Regularly cleaning, heat and chemical treatment are often necessary to avoid the potential development of the bacteria.

  • keep basins and sumps free of mud and organic debris
  • use chemical and organic inhibitors where recommended
  • avoid water stagnation - circulate the water through the system
  • avoid leaks from processes to the cooling water - process water may contain nutrients that may feed the bacteria

The Legionella bacteria cannot survive water temperatures above 131 oF (55 oC) for more than five or six hours. Instantaneous destruction of the bacteria occurs at temperatures above 158 oF (70 oC). General protection against the bacteria in hot water systems can be achieved by designing operating water temperatures to be at least 140 oF (60 oC). Note! - be aware of scalding. Tap water delivered at 140 oF can cause a full-thickness burn in 10 seconds. Hot water should always be mixed down to lower temperature before the tap.

For water temperatures below 140 oF (60 oC) special procedures are required regarding cleaning and chemical treatment.

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  • Engineering ToolBox, (2005). Legionella. [online] Available at: [Accessed Day Mo. Year].

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