Growing in your system
The key to preventing Legionnaires’ disease is to prevent Legionella growth. Legionella can colonize in water delivery lines and building plumbing systems, contaminating water supplies after the water has been centrally treated at a public water facility.
One of the best ways to reduce the risk of Legionella growth is to design, implement and regularly update an overall water safety plan for an entire system, taking into account any potential hazardous conditions for a particular system and including industry best practices for prevention.
Parts of a water system with insufficient circulation or lukewarm temperature can provide the ideal environment for Legionella growth.
Legionella bacteria will grow best between 20°C and 45°C, it will rapidly be killed at temperatures above 60°C, and do not multiply at temperatures above 50°C. They will not multiply at temperatures below 20°C either but can remain alive until the temperature rises to a level allowing multiplication to occur. In addition to appropriate temperatures, Legionella bacteria require nutrients to enable them to multiply. These nutrients are found in the water systems and include other common water organisms, sludge, scale and sediment. Legionella bacteria also require iron to grow, which is often provided by corrosion.
There are several key elements that can promote the growth of Legionella bacteria in a water supply system, including:
- Excessive water age /stagnant water
The longer water sits in a system or piping in a system, the greater likelihood the water disinfectant will dissipate over time, leading to pathogen growth.
When biofilm, a sticky substance created by bacteria, forms on the inside wall of water supply piping, it protects Legionella from heat and disinfectant.
Legionella growth is enabled by lukewarm water temperatures, usually in the range of 77 degrees Fahrenheit to 108 degrees Fahrenheit.
A “dead leg” is caused by no flow or rare flow of water in pipes.
- Insufficient disinfectant
Effective water disinfectant strategies are necessary to control Legionella in a water system. For example, chlorination is one method used by water districts to disinfect drinking water that provides a lasting residual disinfectant.¹
- Inadequate corrosion control
Corrosion can occur in system pipes, depending on several water quality variables, including disinfectants used, water temperature and pH levels. Improper corrosion control can create the ideal environment for Legionella growth.¹¹
Cross connections between potable and non-potable water can introduce Legionella into the potable water supply system.