Legionella is a bacteria that occurs in freshwater environments and is the leading cause of Legionnaires’ disease which causes severe cases of pneumonia. In order to prevent this waterborne risk, it’s important to understand where and how legionella grows as well as what measures can be taken to prevent the bacteria from spreading. 

What Factors Cause Growth 

There is a wide range of external as well as internal factors that can increase the expansion of Legionella such as: 

  • Water Main Breaks
  • Biofilm 
  • Fluctuations in pH 
  • Water Pressure Changes
  • Stagnant Water
  • Construction Debris 

Where Legionella Can Spread 

This dangerous bacteria has the ability to grow within various parts of building water systems especially parts that are continuously wet. Here are several examples of water devices that Legionella can spread across rapidly: 

  • Showerheads 
  • Water Heaters
  • Hot/Cold Water Storage Tanks
  • Misters or Humidifiers 
  • Ice Machines
  • Electronic/Manual Faucets 

Legionella Prevention Methods 

External factors can increase the growth of Legionella within complex water systems in buildings. Therefore, it’s important to monitor several elements of your building water system in order to prevent bacteria expansion before it begins. 


  • Consistently Check Disinfectant Levels. Even the slightest reduction in disinfectant levels can allow Legionella to grow rapidly which is why it’s essential to make sure that levels maintain consistency. Processes such as filtering and heating can potentially reduce the availability of disinfectants such as chlorine, ultraviolet light, and mono-chloramine.


  • Keep Cold Water Cold and Hot Water Hot. It’s crucial to keep water outside of the temperature range for Legionella growth. The bacteria grows best between 77 degrees Fahrenheit to 113 degrees Fahrenheit. Therefore, it’s extremely important to make sure that cold water stays cold and hot water stays hot.


  • Stop Stagnation. Stagnation occurs when water isn’t flowing well which increases biofilm growth, reduces levels of disinfectant, and brings water temperatures to a level that allows bacteria to grow.

Learn more about how to further prevent Legionella through the variety of chlorination services we provide here.