Controlling Legionella Growth in Water Systems
Legionella is the bacterium that causes Legionnaires’ disease. This potentially fatal respiratory illness is caused by a species of Legionella that thrives in piped water systems and cooling towers. The disease is acquired when one inhales fine water droplets containing Legionella bacteria. In this post, we will explore various strategies for controlling Legionella growth in the water systems and the advantages and disadvantages of each method.
Strategies for controlling Legionella growth in water
Strategies for control of Legionella growth in water depends on water chemistry, temperature and the use of the water system.
Legionella growth in water systems can be controlled by using chemicals and modifying the environmental conditions (e.g. by controlling nutrient levels in the water, controlling water temperature, and preventing low flow and stagnation of water).
In some water systems, chemical control of Legionella growth may not be safe because of the system’s design. Therefore, a chemical control strategy should take into account system design, operating parameters and water chemistry (including the potential for production of disinfection by‑products).
The table below shows methods that can be used to control Legionella growth in water systems and the advantages and disadvantages of each method.
Legionella Control Strategy | Advantages | Disadvantages |
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Keeping temperature <20 °C |
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Keeping temperature >50 °C |
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Periodic flushing with hot water at 50–60 °C (usually an essential part of control by high temperature, above) |
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Dosing with sodium hypochlorite |
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Dosing with monochloramine |
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Dosing with chlorine dioxide |
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Dosing with hydrogen peroxide |
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Copper and silver ionization |
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Anodic oxidation |
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UV (ultraviolet) disinfection |
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Ultrafiltration at point of entry to the building or system |
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Point-of-use filters |
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Pasteurization heat with flushing |
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Non-oxidizing biocides |
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Source: LEGIONELLA and the prevention of legionellosis. World Health Organization 2007.
Note: MBL is certified for Legionella analysis. Click CDC Legionella ELITE certification for details.