You might have heard of Legionnaires disease, Legionellosis or Legionella but are not sure of the risks related to your buildings water systems.  A person infected by this disease can develop a serious pneumonia which, in some cases, can be lethal.  According to the CDC, in the US there are 5,000 cases of Legionnaires outbreaks reported yearly in which 1 out of 10 people will die.  In 9 out of 10 cases, these outbreaks were preventable.

In an attempt to assist building owners with cooling tower, we wish to share with you 5 elements to consider to assist in mitigating Legionnaires disease in your building water systems.

Where does this Legionnaire disease come from?  

There are over 25 related species of Legionella bacterium present in nature.  These bacterium are naturally present in streams, rivers, lakes and are relatively harmless.  The serogroup responsible for Legionella disease and which is the most lethal is Legionella pneumophila.  It becomes a serious health concern when present in man-made water systems.

Why is it a serious health issue in man-made water systems and not in nature?

Once this bacterium species becomes airborne by misting of water fountains, evaporation of water in cooling towers or in spas/pools, it has the ability to travel with air currents and infect people relatively near the source of contamination.  Once infected, a serious pneumonia can be developed.

Am I at risk?

All building owners with cooling towers or evaporative condensers for their HVAC&R systems, spas/whirlpools, ornamental fountains, misters and humidifiers are at risk.

What can I do to mitigate my risks?

We’ve listed 5 elements to consider in mitigating your risks:

1. Assessment and analysis of your building water systems: Does your building have any of the items listed as a risk factor (cooling towers, fountains, misters, etc.)?

  • Identify potable and non-potable water systems
  • Locations of these systems.
  • How the water is received and processed.
  • Process flow diagram – identify potential risks in the systems water flow.

2. Water treatment program: 

  • Put in place a water treatment program developed by water treatment professional: Recurring water disinfection is a requirement.  There are high performing, sustainable water disinfection technologies in the market to avoid expensive & recurring chemical cost.  EMO3 can assist you (
  • Ensure no stagnation of water – Legionella thrives in warm waters between 72F to 104F (22C to 40C) and develops in biofilms.   Ensure there are no dead-arms in your water systems and provide adequate water recirculation.
  • Ensure the plan includes a maintenance and contingency plan in case of outbreak.
  • Communication & control: Share the plan with your team and ensure clear responsibility of tasks.

3. Limit the spread of mist from your water systems.  

  • There are numerous solutions on the market that can assist in reducing the mist spray from travelling from your water systems.

4. Control & monitor:

  • Identify monitoring locations in key areas
  • Establish a sampling schedule: There are several user-friendly tools to monitor the bacteria counts in water (agar-based dip-slides, ATP, etc.).  Include a Legionella testing every 30 days of operation.

5. Ask for help:

  • There are numerous water consultants to assist you.  They will develop a plan that reflects your buildings water systems.
  • ASHRAE standard 188: The American Society of Heating, Refrigerating and Air-Conditioning Engineers has released a comprehensive standard regarding Legionellosis risk management.

Have questions or simply need to talk to someone, give us a call at (866) 805-8003 or send us an email at


Dave Gilbert, Eng., MBA

EMO3 inc.