Legionella bacteria can become a health concern when they grow and spread in water systems. These bacteria are naturally present in freshwater environments, like rivers and lakes, usually in low, harmless concentrations. However, they can multiply to dangerous levels in human-made water systems, leading to illnesses such as Legionnaires’ disease, a severe form of pneumonia.
Factors Influencing Growth
Legionella growth in water depends on specific environmental conditions. Temperature is a primary factor, with Legionella growing optimally between 20°C and 45°C (68°F and 113°F). The most rapid growth occurs around 37°C (98.6°F), which is close to human body temperature. Temperatures below 20°C cause the bacteria to become dormant, while temperatures above 60°C begin to kill them.
Water stagnation also contributes to Legionella development. When water remains still in pipes or tanks, disinfectant levels can decrease, creating an environment where the bacteria can multiply undisturbed. Stagnant water, particularly in areas like “dead legs” (sections of piping with no or low flow), allows Legionella to settle and form protective layers. This creates an ideal breeding ground.
The presence of nutrients and biofilm further accelerates Legionella growth. Biofilm is a slimy layer formed by microorganisms that adhere to pipe surfaces and fixtures. This layer provides nutrients and protection, shielding Legionella from disinfectants and making elimination harder. Sediment, rust, and other organic matter in water systems provide food for the bacteria, aiding their growth within these biofilms.
Typical Contamination Sites
Legionella can develop in various human-made water systems with suitable growth conditions. Cooling towers, part of centralized air conditioning, are common sites for contamination due to their large water volumes and temperature fluctuations. Hot tubs and spas also pose a risk, maintaining warm water ideal for growth and producing aerosols.
Large plumbing systems in buildings like hotels, hospitals, and apartment complexes are also susceptible. These systems often have extensive pipework with areas of low flow or infrequent use, leading to water stagnation. Hot water tanks and heaters can harbor Legionella if temperatures are not maintained above the optimal growth range.
Showers and faucets, especially those used infrequently, can accumulate stagnant water and biofilm, increasing bacterial risk. Decorative fountains and misters, which create water aerosols, also present an exposure risk if Legionella is present. Any system that generates water droplets small enough to be inhaled carries a risk if contaminated.
Preventing Bacterial Development
Controlling Legionella development involves managing conditions that foster its growth. Temperature control is a strategy; hot water should be stored above 60°C (140°F) and distributed above 50°C (122°F) to outlets. Cold water systems should maintain temperatures below 20°C (68°F) to inhibit bacterial activity.
Preventing water stagnation is another measure. Regularly flushing infrequently used water outlets, such as showers and faucets, helps introduce fresh water and maintain disinfectant residuals. For outlets not used at least weekly, flushing for several minutes can reduce Legionella risk. Removing “dead legs” in plumbing systems eliminates areas where water can stagnate.
Routine system maintenance, including cleaning and disinfection, is important. This addresses biofilm, sediment, and scale buildup in water tanks, pipes, and fixtures. Regular cleaning of showerheads and aerators helps prevent the accumulation of biofilm. For larger or more complex water systems, implementing a comprehensive water management plan is recommended. These plans involve identifying hazardous conditions, monitoring control measures, and establishing protocols for interventions when issues arise.