Methods for controlling Legionella growth in piped water systems and cooling towers

• Simple, effective and easily monitored
• Little significant growth of Legionella

• Only really applicable to drinking water systems

• Simple, effective and easily monitored

• Does not eliminate legionellae
• Requires circulation temperature to be near 60 °C
• Difficult to maintain temperatures in old systems
• Requires protection against scalding

Periodic flushing with hot water at 50–60 °C (usually an essential part of control by high temperature, above)

• Simple, effective and easy to monitor

• Not applicable in cold-water systems
• Requires protection against scalding
• Must be maintained and inspected to achieve consistent control
• Recolonization occurs within days

• Proven, effective disinfection technique
• Simple to use
• Relatively cheap

• Formation of trihalomethanes
• Needs protection (e.g. carbon filter) for dialysis patients
• Toxic to fish
• Affects taste and odour
• Not stable, particularly in hot water
• Increases corrosion of copper

• More persistent than chlorine
• Simple to use in mains distributions
• Penetrates into biofilms

• Needs protection (e.g. carbon filter) for dialysis patients
• Toxic to fish
• Affects rubber components
• No commercial kit available for dosing small water systems

• Proven disinfection technique
• Simple to use

• Formation of chlorite
• Needs protection (e.g. carbon filter) for dialysis patients
• Safety considerations (depending on method of generation)

• Simple to use

• Weak disinfectant
• Suspected of mutagenicity

• Effective when prescribed concentrations are maintained

• Frequent monitoring of copper and silver needed
• Pretreatment needed (pH, hardness)
• Increased concentrations of copper and silver in water

• Disinfection demonstrated

• Pretreatment needed (depending on effect of pH and hardness)
• Effect on Legionella in biofilms not known

• Proven disinfection technique
• Simple to use

• Effective only at point of application; no control downstream (no residual)
• Not suitable for turbid waters
• No effect on biofilm formation

• Physical disinfection barrier
• Effective removal of biomass and particles

• No inactivation of Legionella downstream of the filter within system
• Effect on formation of biofilms and sediment not known

• Physical barrier
• Easy to install (may require some modification of the outlet)
• Suitable for hot and cold-water systems
• Good for use in systems exposing high-risk patients

• Only suitable at point of use
• Must be replaced regularly
• Particulates in water may reduce flow and operational life
• Expensive

• Disinfection barrier
• Useful as short-term remedial measure
• Simple to apply in hot-water installation

• Transient effect on Legionella
• No limitation of biofilm formation
• Scalding risk

• Proven technique for cooling systems

• Not suitable for potable water systems
• Most not applicable to spa pools
• Resistant populations may develop
• Need to alternate two different biocides
• Often concentrations cannot be readily monitored
• Difficult to neutralize for sampling purposes