Legionella: Do you have a Plan?

Nov 5, 2021

Legionella is a bacterium that can be found outdoors in freshwater environments. As we discussed in a previous blog, The Basics of Legionella, it can find its way indoors through the plumbing and mechanical systems. This bacteria becomes a health hazard when water containing high concentrations gets aerosolized and inhaled. In this blog post, we will emphasize the importance of having a plan to prevent a deadly Legionnaires’ Disease outbreak in your building.

Legionella: Health Effects & Sources

Legionella bacteria are responsible for causing Legionnaires Disease and Pontiac fever. Legionnaires’ Disease is a pneumonia that is accompanied by flu-like symptoms including fever, cough, and muscle aches. Typically, those at a higher risk of getting sick are the elderly, smokers, and people with weakened immune systems. Currently, a vaccine is not available that can prevent Legionnaires’ disease. According to the CDC, the cases of Legionnaires’ disease are increasing.

For the bacteria to be transmitted into the lungs, contaminated water must be aerosolized. The water contaminated with Legionella can come from various sources including hot tubs, decorative fountains, cooling towers, showerheads, and sink faucets. It is also worth mentioning that a typical home is at lower risk for Legionella due to the regular use of hot water and the lack of cooling towers in the air conditioning process. Also, the hot water piping systems of homes are generally less complex.

Legionella: Water Management Plans

To reduce the risk of contracting Legionnaires’ Disease, large buildings should implement a water management plan. This is likely something new for building engineers and property managers, so there is often reluctance to set this up if it is not required by law. In general, a water management plan includes the following:

  • Description of the building water systems
  • Identification of areas where Legionella growth is possible
  • Implementation of control measures
  • Monitoring of control measures
  • Plan of action when control limits are not met
  • Evaluating the effectiveness of the water management plan

For buildings wanting to develop a plan of action for Legionella, two key resources are the CDC toolkit and ASHRAE Standard 188 Legionellosis: Risk Management for Building Water Systems. The best water management plans, in our opinion, are those that require quality control testing of Legionella in the water. A company like Indoor Science can collect samples from the risky areas identified in the water management plan including cooling towers, water filters, decorative fountains, or from domestic water supplies. Without actually monitoring Legionella levels in water systems, it is difficult to know if the plan is actually working.

Legionella: Factors your Plan Must Consider

As building engineers work to develop a water management plan they should consider a few factors when evaluating risks for Legionella contamination. One key factor is water temperature. Legionella’s optimal temperature for growth occurs between 77°F-108°F, with an ideal temperature around 100°F.  This makes temperature fluctuations in a building’s water system an important parameter to log. A heavily-used hot water line at 120°F isn’t at risk, but a rarely used neighboring pipe might sit stagnant at an ideal 100°F.

Another factor to consider is the presence of biofilm, which can allow Legionella to evade the residual water treatment chemicals in water. Biofilm is basically slime that can adhere to different continuously damp surfaces.  Biofilm can harbor Legionella growth with research showing that it can grow inside other organisms such as amoebae. Additionally, water pressure changes in pipes can dislodge biofilm from one area and move it down the plumbing system to a different area. Stagnant water can also lead to biofilm growth. Even changes in pH can render some disinfectants inadequate and allow Legionella to grow. The point here is that even a building with potable, disinfected water can harbor Legionella, so all buildings need to take action.


Facility managers and building engineers have a lot of responsibilities. Therefore, most buildings only consider developing a water management plan when it’s too late and someone is sick with Legionnaires’ Disease. As Benjamin Franklin said, “By failing to prepare, you are preparing to fail.”

A company like Indoor Science can be a great resource to help you implement a water management program along with regular monitoring via water sampling.