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Cooling Towers: Preventing Legionnaires Disease and Mitigating Risk

Most people give little thought to the risks of a water and airborne diseases, but since 2000, cases of Legionnaires’ disease have increased 400%! Learn what code authorities can do to help reduce the risk.

Water Cooling Towers

August 21, 2019

The last time you walked through a hotel, passed a public fountain or visited a Health Care facility did you consider what keeps you safe from water or airborne diseases that often cause serious illness or even death?

Most people give little thought to these risks, but since 2000, cases of Legionnaires’ disease have increased 400%!i More troubling is the fact that 10% of those contracting the disease will die from it. The risk is even greater for those in a health care facility: in this setting, the rate of death increases to 25%.ii

There are many instances illustrating the impact that a Legionnaires’ disease outbreak can have on a structure and its patrons. For example, summer 2015 saw an outbreak of Legionnaires’ disease in the South Bronx that was attributed to Legionella-contaminated cooling towers. Nearly 140 cases were confirmed, resulting in 16 deaths.iii Additionally, 15 cases of Legionnaires’ disease were identified in Flushing, N.Y. (New York City area) in October 2015. City health investigators ordered disinfection of several cooling towers where Legionella was found.iv  One of the challenges with these outbreaks is that many individuals may not be report their illnesses, or their illnesses are misdiagnosed, which likely pushes the actual numbers for each outbreak higher.

As a result of the Legionella outbreak of 2015 in New York, both New York city and state issued rules and regulations requiring owners of buildings with cooling towers to manage the risk of Legionella outbreaks.

Both New York city and state have created requirements for the maintenance of cooling towers. All of these require development, implementation and documentation of a maintenance program and plan (MPP). As a result of these requirements, UL has recently developed a comprehensive, practical and efficient way of working with building owners to determine cooling towers safety.

Unfortunately, the laws regulating cooling towers overlap; can be confusing, time consuming, complicated, and – if not met by the building owner – can result in heavy fines. It is estimated that over $20 million in fines were levied against building owners from 2016 to 2017. UL’s service eliminates the need for building owners or property managers to navigate through these requirements and delivers confidence to building inspectors that a building meets local guidelines.

Benefits of UL’s cooling tower service for code officials

To address the health risk associated with of Legionnaires’ disease, the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) published ANSI/ASHRAE 188, Legionellosis Risk Management for Building Water Systems in June 2015. This first industry consensus standard for managing building water systems to prevent Legionnaires’ disease established a new standard of care.  

UL has established a water quality audit program for building cooling towers. This program offers confidence to building inspectors that maintenance program and plans are being followed by regular program audits to help reduce the likelihood of a Legionnaires outbreak. This UL program also confirms that best practices in ANSI/ASHRAE 188 are met and applicable regulations are followed.

Benefits of a third-party audit of cooling towers for building owners

An effective MPP can significantly reduce the likelihood of a Legionnaires outbreak.  UL’s auditing process provides a practical and efficient way of minimizing risk to public health and safety by determining that an MPP is implemented and continuously followed.  

For more information, please contact [email protected].


  1. [i] Christian Nordquist, 17 July 2017, “Legionnaires disease: What you need to know”, Medical News Today

  2. [ii] CDC “Legionnaires Disease: A problem for Health Care Facilities” taken from

  3. [iii] CDC “Legionnaires’ Disease Outbreak Caused by Endemic Strain of Legionella pneumophila, New York, New York” taken from

  4. [iv] Recent Legionnaires Disease Outbreaks taken from