Legionella control in water systems is essential wherever water is stored, circulated, or sprayed. Although Legionella bacteria are naturally present in many water sources, health risks can arise when favourable conditions are created within man-made water systems. Consequently, proper monitoring, maintenance, and disinfection measures should be implemented to reduce the risk of contamination.
Legionella is a genus of bacteria that includes Legionella pneumophila, the species most commonly associated with human illness. When contaminated water droplets are inhaled, a severe form of pneumonia known as Legionnaires’ disease can be contracted. In addition, a milder illness known as Pontiac fever may be experienced.
Where Legionella Is Found in Water Systems
Legionella bacteria are commonly found in natural water sources such as rivers, lakes, and streams. However, the greatest risks are presented when the bacteria are allowed to multiply within engineered water systems.
Typical locations where Legionella may be found include:
- Hot water storage tanks and geysers
- Cooling towers and HVAC systems
- Decorative fountains
- Hot tubs and spas
- Shower heads and taps
- Humidifiers and misting systems
As a result, regular inspections should be conducted and stagnant areas should be eliminated wherever possible.
Legionella Control in Water Systems Through Monitoring
In order to determine whether Legionella is present, water samples can be collected and analysed. Several testing methods are available.
These methods include:
- Laboratory culture testing
- PCR analysis
- Rapid screening tests
- Routine water quality monitoring
Furthermore, trend analysis can be performed so that developing problems may be identified before an outbreak occurs.
Temperature Management for Legionella Prevention
Temperature control is regarded as one of the most effective methods of Legionella prevention.
The following guidelines are generally recommended:
- Hot water should be stored at temperatures above 60°C.
- Circulating hot water should be maintained above 50°C.
- Cold water should be kept below 20°C.
- Thermal disinfection may be carried out periodically using water heated to approximately 70°C.
By maintaining these conditions, bacterial growth can be significantly reduced.
Chemical Treatment Methods
Where additional protection is required, chemical disinfection systems can be employed.
Common treatment options include:
- Chlorination
- Monochloramine dosing
- Chlorine dioxide dosing
- Copper-silver ionisation
- Ozone treatment
- Ultraviolet disinfection
Although UV systems can be highly effective, no residual protection is provided. Therefore, they are often used alongside other treatment methods.
Maintenance and Biofilm Control
Biofilms, scale deposits, and accumulated sediment can provide ideal environments for Legionella growth. Consequently, routine maintenance should be carried out.
Recommended practices include:
- Regular flushing of rarely used outlets
- Cleaning of storage tanks
- Descaling of pipework
- Removal of dead legs and stagnant sections
- Replacement of deteriorated fittings
Because biofilms can protect bacteria from disinfectants, physical cleaning should not be overlooked.
Ongoing Prevention Is Essential
Even after successful treatment, Legionella can rapidly recolonise a system if favourable conditions return. Therefore, a comprehensive management programme should be implemented. Water quality should be monitored, temperatures should be controlled, and maintenance schedules should be followed consistently.
Through proper design, routine monitoring, and effective treatment, the risks associated with Legionella can be significantly reduced, thereby helping to protect building occupants and maintaining safe water systems.
