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WATER TREATMENT


Reducing the risk of Legionella


Following a recent rise in reported Legionnaires’ disease cases in London, the need for robust water system management has come into sharp focus in commercial buildings. While Legionella bacteria are naturally present in water, poorly designed or inadequately maintained services can allow them to multiply, posing a serious risk to public health. Jason Cox, sales director at Wilo UK, explains the key best practice measures that support safer, more resilient water networks and help protect public health


Supporting water flow A fundamental rule to stopping Legionella bacteria from growing in water systems is to prevent stagnation. Static or infrequently used water creates ideal conditions for bacterial growth, particularly in large, complex or intermittently occupied properties. At a system level, effective design is essential.


Water networks should be configured to encourage regular circulation and avoid areas where water can sit unused for extended periods. Pumping solutions that support consistent movement play an important role in maintaining flow across the installation, even during periods of low demand. Choosing pumps that are specifically designed


for hot water applications is key here, as they help to maintain circulation efficiently while minimising energy consumption. By supporting continuous movement within the system, these solutions form a strong foundation for effective water hygiene management.


Controlling water temperature


Effective temperature control is critical in minimising the risk of Legionella. The bacteria multiply most readily in water temperatures between 20°C and 45°C, making it important to design and operate services that remain outside this range wherever possible. To reduce risk, hot water should be stored at 60°C or above and distributed at no less than 50°C at outlets, while cold water should be maintained below 20°C. Achieving this consistently can be


Left: Jason Cox, sales director at Wilo UK


actively managed through targeted flushing and circulation strategies.


It is important to note that size alone is not a


challenging in buildings with long pipe runs, variable demand or heat loss, making careful system design essential. Well-designed and correctly sized circulation


systems help preserve temperature stability throughout the network. High-efficiency solutions such as Wilo’s Stratos MAXO-Z support continuous hot water circulation, reducing temperature drop- off in seldom used areas. For smaller systems or decentralised applications, Stratos PICO-Z and Yonos PICO-Z provide reliable circulation with low energy input.


Removing dead legs


Poorly circulated sections of pipework (‘dead legs’) create ideal conditions for bacterial growth and should be eliminated where possible. This is an essential step in managing Legionella risk. Where possible, dead legs should be designed out at the specification stage through simplified layouts and efficient routing. In retrofit projects, removal may not be feasible, and these sections must be


safeguard. Pipe sections as short as 25cm can become problematic if left unmanaged. Ensuring consistent water movement is therefore critical, particularly in buildings with seasonal use or varying occupancy patterns. Properly specified circulation pumps play a key role in preventing water from sitting idle within these vulnerable areas of the system.


Flushing regularly


Routine flushing forms a core part of any effective Legionella control strategy. Flushing outlets and pipework can maintain water movement, refresh system temperatures and disinfectant levels, and prevent the build-up of stagnant water where bacteria can thrive. Again, this is particularly important in buildings with infrequently used outlets or those subject to periods of reduced occupancy. After extended shutdowns or vacancy, thorough


system flushing with hot water at 60°C or above is essential to restore safe operating conditions before full reoccupation. Flushing regimes are most effective when supported by reliable circulation and stable pressure, ensuring hot water reaches all parts of the network quickly and consistently. Ultimately, reducing Legionella risk depends on effective design, consistent maintenance, and ongoing monitoring to safeguard public health.


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