Legionella Prevention in Cooling Tower Systems

With the support of a team of experts, managers can effectively prevent, detect and respond to positive Legionella tests.

By Anthony Caruso

Healthcare facility managers are familiar with Legionella bacteria — the cause of Legionnaire's disease and Pontiac fever — and its harmful effects in healthcare facilities, especially those with inpatient units. Managers are charged with ensuring that facility water systems are maintained and chemically treated to prevent the bacteria’s growth, so managers responsible for operating cooling towers should be aware that the Legionella bacteria can grow in and be aerosolized through the cooling towers. 

Given the risk of this occurring in an environment in which patients already might be experiencing health issues, managers should make it a top priority to prevent bacteria growth by developing a game plan and implementing best practices for controlling and monitoring Legionella in cooling towers. 

Planning for trouble 

Facility managers need to be familiar with the facility’s central chiller plant and its equipment, and consulting with equipment operators is a best practice. Managers must have schematics of the plant for their reference, and it is imperative that they understand the water on the condensing loop is not potable and is not delivered to water fountains or sinks in the facility. 

The facility management team should maintain and regularly review the cooling tower management plan, which is also the game plan for Legionella prevention and should accurately describe the response in the event of a positive test in the cooling tower. 

The plan is comprised of engineering actions, such as increasing the frequency or amount of chemical treatment. The maintenance team should verify that all equipment is running properly.  

Communication regarding a positive test should be clear and concise. The water safety team should create a simple, straightforward message for facility leadership, and the facility manager plays a vital part in composing the message. 

Another best practice is to have a set period in which a retest will occur. The plan can include equipment listing, testing limits and a risk assessment for the particular environment. It is important to note that the plan is a requirement for all Veteran’s Affairs (VA) Medical Centers under the guidance from the Veterans Healthcare Administration (VHA) Office of Healthcare Engineering and VHA Engineering Standard-2019-001 Cooling Tower Water Systems.  

Preventing, treating and responding to Legionella in cooling towers is not an individual endeavor. For instance, the Coatesville VA Medical Center has a Water Safety Committee comprised of healthcare executives, an environmental specialist, occupational safety specialists, engineering personnel, and maintenance personnel. The team consults each other on water safety matters and new regulations, and it reviews testing results. The team will always assemble in the event of a positive test at our facility. 

Preventive maintenance inside and outside the chiller plant also is crucial. The facility engineer is responsible for equipment handling water at the source, such as pumps and chemical treatment feeders. Our facility uses our well for the water supply but has an interconnection with the municipal water in case of equipment failure, but the municipal water uses a different chemical treatment. 

Best practices 

Savvy facility managers understand the variables within their systems and have contingencies for each situation. Within the plant, managers must pay close attention to the maintenance and operation of the chillers, pumps, chemical feeders, controls and cooling towers. Changing or cleaning of the cooling tower drift-elimination panel must occur regularly to ensure scale does not build up. 

Cooling towers also can be outfitted with supplemental equipment that ensures they do not spread Legionella to adjacent facilities. The aforementioned drift eliminator is a plastic membrane that catches excess chemicals as the water turns to vapor and directs aerosolized water upward, rather than laterally. A properly working drift eliminator ensures vapors dissipate without reaching adjacent facilities. Second, walls protecting the cooling towers from prevailing winds will keep the vapor out of nearby windows, HVAC louvers and other openings. 

Chemical treatment for cooling tower systems is required. In the Veterans Health Administration, the Engineering Standard ES-2019-001 Cooling Tower Water Systems dictates that biocides, such as chlorine and bromine, are used to chemically treat the water and keep the Legionella bacteria count below allowable limits. 

One best practice is to have an external company maintain the chemical feeder equipment and act as a third-party consultant on these matters. It is important to bear in mind that chemical treatment will be the primary response when Legionella is detected in the system. 

Administrative means can assist managers with prevention and early detection of Legionella in cooling tower systems. Constant, regular testing is the most effective way to determine if the plan elements listed above are effective. Testing includes chemical residuals and the presence of the bacteria causing Legionella. 

Positive bacteria results also might indicate equipment failure. In severe Legionella contamination cases, utility or plant shutdowns might be necessary. In very critical cases, managers might need to secure the chiller plant until further notice. 

Managers should prepare for the use of a temporary chiller or cooling tower in the event the Legionella cannot be treated and controlled in short order. In these situations, managers must consider the following questions: 

  • Does the chiller plant have a connection for a temporary cooling tower? 
  • Does the manager have a procurement vehicle in place to rapidly employ a temporary cooling tower? 
  • Does the chiller plant facility have the space and security measures for a temporary cooling tower? 
  • Does the chiller plant have the electrical capacity and a connection for the temporary equipment? 
  • What is the equipment redundancy in the chiller plant? Can the facility run on one cooling tower until the bacteria can be reduced?  

These severe situations and associated contingencies emphasize the importance of the facility manager’s strong working knowledge of the chiller plant and its associated components. A manager’s role in maintaining the cooling towers to prevent Legionella cannot be understated. With the support of a team of experts, managers can effectively prevent, detect and respond to positive Legionella tests using this game plan. 

Anthony Caruso, P.E., PMP, is the chief engineer at the Coatesville, Pennsylvania, U.S. Department of Veterans Affairs Medical Center. He is a U.S. Army veteran and a degreed civil engineer. 

September 28, 2022

Topic Area: HVAC , Infection Control

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