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  • Lisamarie Lamb

Common Mistakes in Legionella Control and How to Avoid Them

Legionella control is a critical aspect of maintaining a safe and healthy water system, whether in residential, commercial, or industrial settings. Despite best efforts, common mistakes can compromise the effectiveness of legionella prevention measures. This blog post highlights some of these mistakes and provides guidance on how to avoid them.

Inadequate Risk Assessments

One of the most significant mistakes in legionella control is conducting inadequate or infrequent risk assessments. Risk assessments are essential for identifying potential legionella hazards in a water system. However, some organizations fail to conduct thorough assessments, overlooking critical areas where legionella could thrive.

How to Avoid It: Ensure that risk assessments are comprehensive and carried out by qualified professionals. Regularly update these assessments, especially after any changes to the water system or building structure.

Poor Temperature Control

Legionella bacteria thrive in water temperatures between 20°C and 45°C (68°F and 113°F). Poor temperature control, where water temperatures fall within this range, can lead to bacterial growth. Both hot and cold water systems must be appropriately managed to prevent this.

How to Avoid It: Maintain hot water systems at temperatures above 60°C (140°F) and ensure that cold water stays below 20°C (68°F). Regularly monitor and record water temperatures to ensure compliance with these guidelines.

Inadequate Water Treatment

Water treatment is essential for controlling legionella, but inadequate or improper treatment can render these efforts useless. This includes the use of incorrect biocides, poor dosing, or irregular treatment schedules.

How to Avoid It: Implement a robust water treatment program tailored to your specific system. Use appropriate biocides and ensure they are dosed correctly and consistently. Regularly review and adjust the treatment program as necessary.

Neglecting Regular Maintenance

Regular maintenance of water systems is crucial in preventing legionella outbreaks. Neglecting maintenance tasks such as cleaning and descaling can lead to the accumulation of biofilm, scale, and other materials that promote bacterial growth.

How to Avoid It: Establish a routine maintenance schedule that includes cleaning, descaling, and inspection of all water system components. Ensure that maintenance tasks are documented and performed by trained personnel.

Ignoring Stagnant Water

Stagnant water provides an ideal environment for legionella to grow. Systems with infrequent use or areas with low water flow can become breeding grounds for the bacteria.

How to Avoid It: Design water systems to promote continuous flow and avoid dead legs where water can stagnate. In areas with infrequent use, implement a flushing regime to ensure fresh water circulates regularly.

Lack of Staff Training

Even the best Legionella control measures can fail if staff are not adequately trained. Without proper training, staff may not understand the importance of control measures or how to implement them correctly.

How to Avoid It: Provide regular training for all staff involved in water system maintenance and Legionella control. Ensure they understand the risks, control measures, and their role in maintaining a safe water system.


Avoiding these common mistakes in legionella control requires diligence, proper planning, and ongoing education. By conducting thorough risk assessments, maintaining appropriate water temperatures, implementing effective water treatment, performing regular maintenance, preventing water stagnation, and training staff, you can significantly reduce the risk of legionella in your water system.

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