Legionella is a persistent threat in buildings, regardless of their age. Both new constructions and old structures are at risk. While over 40 species of Legionella exist, Legionella pneumophila is the most concerning, responsible for approximately 90% of infections.

How Legionella Becomes a Problem

Legionella bacteria are naturally present in various water sources, such as lakes, rivers, and soils. Inevitably, they find their way into building water systems, regardless of the precautions taken. Initially entering in low numbers, the real danger arises when these bacteria begin to grow and multiply. If allowed to proliferate, Legionella can become a severe health risk, particularly when dispersed through aerosols or fine water mists, which are then inhaled.

There are three primary stages where Legionella becomes a problem:

1. Intrusion: Legionella enters the water system.
2. Growth: The bacteria multiply within the system.
3. Transmission: Infected aerosols or water droplets are inhaled, leading to potential health risks.

How Legionella Enters Building Water Systems

Research indicates that drinking water systems are the primary source of Legionella bacteria and Legionnaires’ disease. Since Legionella occurs naturally in freshwater environments, it’s almost impossible to prevent its initial entry into a water system. However, the bacteria pose a threat when they grow and spread in man-made water systems, including:

• Showerheads and sink faucets
• Cooling towers
• Hot tubs
• Decorative fountains
• Hot water tanks and heaters
• Large, complex plumbing systems

Legionella bacteria often reside in the biofilm and corrosion within pipes. Routine disruptions to public water systems, such as water main breaks or fire hydrant use, can release this biofilm into the water supply, increasing the risk of contamination.

Effectively managing water systems is crucial to minimizing this risk.

Preventing Legionella Growth

The key to preventing Legionnaires’ disease is to control Legionella growth in water systems. Even after water is treated at a public facility, Legionella can colonize in water delivery lines and building plumbing systems. To mitigate this risk, it’s essential to design and implement a comprehensive water safety plan that accounts for potential hazards and adheres to industry best practices.

Legionella thrives in environments with specific conditions:

• Temperature: Optimal growth occurs between 20°C and 45°C. Above 60°C, Legionella is rapidly killed, and it does not multiply below 20°C, though it can survive until temperatures rise again.
• Nutrients: Legionella feeds on other organisms, sludge, scale, sediment, and iron from corrosion, all of which are commonly found in water systems.
• Stagnant Water: Prolonged water stagnation can lead to disinfectant dissipation, increasing the likelihood of Legionella growth.
• Biofilm: This sticky substance forms on pipe walls, protecting Legionella from heat and disinfectants.
• Dead Legs: Sections of piping with little to no water flow create ideal conditions for Legionella.
• Insufficient Disinfectant: Effective disinfection, such as chlorination, is necessary to control Legionella.
• Inadequate Corrosion Control: Corrosion can promote Legionella growth if not properly managed.

Control Methods to Prevent Legionella

To prevent Legionella growth, consider implementing the following measures:

• Cold Water Management: Ensure cold water is stored and distributed below 20°C to discourage bacterial growth.
• Hot Water Management: Store hot water at 60°C and distribute it above 50°C to outlets within one minute.
• Reduce Stagnation: Introduce routine flushing programs and minimize stored water volumes.
• Chemical Control: Use chemical treatments as a last resort, focusing first on fundamental control and management measures.

Responding to Legionella in Your Water Supply

Discovering Legionella in your building’s water system doesn’t necessarily indicate an outbreak, but it does require further investigation to identify the source and extent of contamination. Building water systems typically draw from the public drinking water supply, which may occasionally contain bacteria. Effective water management practices should neutralize most threats. However, significant disruptions to the public water system can introduce large volumes of contaminants, potentially overwhelming the system’s defenses.

By understanding the risks and implementing comprehensive prevention strategies, building owners and managers can significantly reduce the chances of Legionella contamination and protect the health of occupants.