In this post, we explore some of the common Legionella risk factors to help you assess your building’s vulnerability.

Legionnaires’ disease is a serious public health concern caused by the Legionella bacteria. The bacteria thrives in various water systems and damp environments. Inhaling aerosolized water droplets containing Legionella can lead to respiratory illnesses. Hence it is has become crucial for buildings to conduct a Legionella Risk Assessment to identify any contamination or risks posed.

Legionella: Understanding the enemy

The Legionella bacteria is naturally present in water sources like rivers and lakes. However, they can become problematic when they infiltrate into man-made water systems.

The common areas for Legionella contamination in buildings include:

1 – HVAC Systems: Air conditioning systems can disperse Legionella-contaminated droplets into the air, putting occupants at risk.

2 – Hot Water Systems: Legionella can multiply in hot water tanks and pipes, especially when the water temperature is not properly maintained.

3 – Cooling Towers: These are common in large buildings and industrial facilities. The warm, moist environment inside cooling towers is an ideal breeding ground for Legionella.

4 – Spas: Water in hot tubs and spas can become a reservoir for Legionella.

Assessing Legionella Risk in Your Building

Now that you understand where Legionella might be lurking, let’s examine the risk factors that could make your building vulnerable:

1. Age and Design of the Building: Older buildings with complex plumbing systems are more likely to have stagnant water areas where Legionella can grow. Buildings with intricate designs and numerous water features may also pose a higher risk.

2. Temperature Control: Legionella thrive in water temperatures between 77°F to 108°F (25°C to 42°C). Ensure that hot water systems maintain water temperatures above 140°F (60°C) to prevent Legionella growth. On the other hand, cold water systems should remain below 68°F (20°C).

3. Water Quality: Poor water quality, including the presence of sediment or biofilm, can provide a breeding ground for Legionella. Additionally, a pH level outside the range of 6.5 to 8.5 can encourage their growth.

4. Infrequent Water Usage: Buildings with low water usage, such as vacant properties or those with seasonal occupancy, can experience stagnant water in pipes, which increases Legionella risk.

5. Lack of Maintenance: Neglected maintenance of cooling towers, HVAC systems, and hot water tanks can lead to the accumulation of organic matter and biofilm, creating an ideal environment for Legionella.

6. Nearby Construction: Construction work can disturb water systems and introduce contaminants. Be vigilant if your building is located near active construction sites.

7. Occupant Vulnerability: Consider the health and age of building occupants. Elderly individuals and those with compromised immune systems are at higher risk of Legionnaires’ disease.


Understanding the Legionella risk factors that could affect your building is the first step toward prevention. Regular maintenance, water quality management, and vigilance can significantly reduce the risk of Legionella contamination. Protecting the health and safety of building occupants should always be a top priority, and awareness of Legionella risk is a crucial part of that effort.

Conducting a Legionella Risk Assessment

At URS Testings Laboratory, our Legionella experts can help you conduct a risk assessment of your premises or building to help ascertain any legionella risks present and advise solutions to mitigate or eliminate the same.