Legionella bacteria occur naturally in many environments, including lakes, rivers, and soil. Because of this, it’s almost inevitable that small amounts of Legionella will enter a building’s water system — no matter how carefully it’s designed or maintained.
However, while their presence in low numbers is not usually a concern, problems arise when Legionella begin to grow and multiply. Once this happens, and if the bacteria become airborne through aerosols or fine water mists, they can pose a serious health risk.
That’s why effective water system management is essential to minimise risk and prevent bacterial growth.
The Three Key Factors Behind Legionella Risk
- Intrusion – Legionella enter the water system.
- Growth – The bacteria multiply within the system.
- Transmission – Aerosols or small droplets containing Legionella are inhaled.
How Legionella Enter Your System
Research has shown that drinking water systems are the primary source of Legionella bacteria and Legionnaires’ disease. The risk increases in complex, human-made systems such as:
- Showerheads and sink faucets
- Cooling towers (used in central air cooling systems or industrial processes)
- Hot tubs and spas
- Decorative fountains and water features
- Hot water tanks and heaters
- Large or complex plumbing systems
Contamination typically occurs when water systems are poorly maintained, allowing conditions that support bacterial growth to develop.
How Legionella Grow
Preventing Legionella growth is the most effective way to protect your water systems. Even after water is treated at a public facility, Legionella can colonise pipes and plumbing systems within buildings, especially in areas where:
- Water circulation is poor or stagnant
- Temperatures are within the optimal growth range
Legionella bacteria thrive between 20°C and 45°C, stop multiplying above 50°C, and are rapidly killed above 60°C. They can survive at temperatures below 20°C but remain dormant until conditions become favourable again.
The bacteria also need nutrients — such as other microorganisms, sludge, scale, and sediment — and iron, often supplied by pipe corrosion, to support their growth.
Controlling Legionella Growth
Several key control methods can significantly reduce the risk of Legionella proliferation:
- Temperature Control
Cold Water: Store and distribute below 20°C. Water should reach all outlets at this temperature within two minutes of opening the tap.
Hot Water: Store at 60°C and deliver to all outlets above 50°C within one minute of operation.
- Prevent Stagnation
Introduce routine flushing programmes and minimise stored water volumes to prevent stagnant conditions where bacteria can grow.
- Chemical Control
Chemical treatment should always be the last line of defence. Before implementing any chemical programme, explore fundamental control and management measures to address the root causes of contamination.
Conclusion
Everyone expects safe, clean water when they turn on the tap — but maintaining water safety can be challenging. Ageing infrastructure, modern plumbing designs, and reduced water flow rates can all contribute to conditions that allow Legionella to thrive.
While it’s impossible to prevent Legionella from entering your water system entirely, effective management and monitoring can stop it from multiplying and spreading.
Our in-house microbiologist and expert team provide tailored advice and precise recommendations to help you keep your water systems safe and compliant.
Contact us today to learn more about how we can protect your water supply from Legionella risks.