A Few Thoughts about Controlling the Risk of Legionella

A few thoughts about controlling the risks of waterborne pathogens, specifically Legionella

In the US, drinking water supplies are thought of as the safest in the world. However, like anywhere else, the water can be contaminated and requires the appropriate water treatment methods to remove disease causing agents. Common forms of waterborne pathogens and bacteria are cryptosporidium, E. coli, Hepatitis A, Giardia intestinalis, Legionella and other pathogens. Municipal and public drinking water systems use various methods of water treatment to provide safe and clean drinking water in the community water systems. However, when a new pathogen or bacteria with potential risk for disease and injury is discovered it takes a long time to figure out the best approach for prevention and safety.

For example, the discovery of Legionnaires’ Disease was 40 years ago but it was only recently a wide spread level of agreement among government agencies, Legionella experts and industry groups on the approach to legionella prevention in our domestic potable water systems was established. This article will examine the key facts that is agreed upon across the industry regarding Legionella prevention, as well as the key action points outlined in water management plans for preventing legionella and other waterborne diseases.

Key facts agreed upon across the industry (in bullet points):

  • Legionnaires’ Disease is contracted through respiration by inhaling droplets of water contaminated with legionella into a person’s lungs
  • Exposure points are anywhere water mist is produced like showers, sinks, water fountains, cooling towers etc. where persons can inhale and get water droplets into their lungs
  • Legionella is costly and wide spread. Almost 8,500 Legionella cases were reported by the CDC in 2018. In 2010 the Center for Disease Control and Prevention (CDC) reported Legionella as the number one cause of water borne disease outbreaks in America and the most expensive. For example, the Illinois Department of Veterans’ Affairs recommended replacing the Illinois Veterans Home in Quincy with a state-of-the art facility at a cost of $278 million as a way to eradicate Legionella from the facility. (Click here to see the original article)
  • Direct healthcare costs amount to hundreds of millions of dollars annually. (CDC 2010. “Waterborne diseases could cost over $500 million annually in US”)
  • Legionella prevention must begin in building water systems which is where the legionella bacteria cultivate. Most government agencies and industry groups that have issued a Legionella guidance document agrees that building water systems must be managed to minimize outbreaks.
  • The wide spread level of agreement is illustrated in the reiterated suggestion that it is the facility manager or owner’s responsibility to develop a water management plan in reports like the World Health Organization’s “Legionella and the prevention of Legionellosis”, the U.S. Veterans Health Administration’s 1061 Directive, and the ASHRAE 188p.


Despite the varying terminology these reports describe the same components in their water management plans. Actions recommended to facility managers and owners for prevention of Legionella and other waterborne pathogens include these key action points:


  • A water management team that oversees the plan and makes decisions to address any weaknesses or issues.
  • Building water system information and flow diagrams that outline key information about the water systems and illustrate water flow from the street to each of the systems and points of use within buildings.
  • A hazard analysis finding weak points in the system which make up a greater potential for Legionella growth and transmission.
  • Control measures, particularly in areas defined as weak points. The goals is to take evidence-based and effective steps to minimize risk. A procedure monitoring the performance of each control measure must also be included in the corrective actions against signs of Legionella growth.
  • Verification procedures ensuring that the water safety plan is implemented.
  • Validation method(s) to show the effectiveness of the plan in controlling Legionella.


These facts and key action points are what is currently shaping new legislation and standards for water management plans across the country.  Facility owners and managers are wise to take action by developing and implementing a water safety plan. This way building operators are minimizing health and legal risk and continuing to improve US drinking water supplies keeping them among the safest in the world.

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