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Legionella in Empty Office Buildings

Legionella testing in cooling tower

For almost a year, many people who used to commute to an office are now working from home due to the global pandemic. This means that many large and small buildings have been mostly vacant for months.  It may seem that a less occupied building does not need as much support from maintenance or building engineers because there are less people. The truth is that buildings still require regular maintenance. One particular environmental hazard to look out for in vacant buildings is Legionella bacteria. 

Legionella Basics

Legionella is a type of bacteria that is naturally found in freshwater environments such as ponds and lakes.  It can cause a respiratory disease in humans called Legionnaires’ Disease when water droplets that contain Legionella bacteria are aerosolized and inhaled by the lungs. Those with compromised or weakened immune systems and the elderly are more susceptible in contracting Legionnaires’. To learn more about the basics of Legionella, read our previous blog post.  

While Legionella is naturally found in outdoor environments, it becomes potentially hazardous when it is present in indoor water systems. In plumbing, Legionella typically begins to multiply in stagnant water, preferring a temperature range of 77°F-108°F (Cite 1). Using water contaminated with Legionella for decorative fountains, cooling towers, or humidifiers can drastically increase the risk of a person contracting Legionnaires’ because the contaminated water is aerosolized and can be inhaled. 

Re-Opening Strategies

Several steps can be taken to prevent water systems in a building from generating Legionella bacterial growth. One seemingly obvious mean to prevent Legionella bacterial growth is flushing water fixtures regularly. Flushing fixtures becomes more essential when buildings are mostly vacant, as they are now during the pandemic. Before the pandemic, the occupants of a building used toilets, sinks, or showers constantly. With so many people working from home, it becomes the maintenance staff and building engineers’ responsibility to regularly flush water fixtures. Cooling towers also need to be flushed and monitored regularly. Keeping cooling towers free from Legionella can protect both maintenance workers and others occupying the building. 

Other methods such as maintaining water outside of the optimal temperature range for Legionella growth, monitoring pH levels in cooling towers, and draining water from a water heater can also help prevent the bacteria from forming. The Centers for Disease Control and Prevention (CDC) developed helpful recommendations for buildings to safely reopen after a prolonged shutdown or reduced occupancy. It is worth going through the website as it not only provides information on Legionella but also on metals such as copper and lead in water or mold and moisture in the building after a temporary shutdown.


How do you know if the measures you have taken are effective? Develop a water system management plan that includes monitoring pH levels, temperature, the frequency water systems are flushed, and water sampling from different sources. Many buildings develop an in-house monitoring system/schedule and hire an outside third party like Indoor Science to collect samples periodically. By doing some preventative maintenance while buildings are vacant and routinely testing water sources, a building can safely reopen and prevent Legionella from causing yet another respiratory disease. 

Ian Cull

Ian Cull is a nationally recognized expert in the field of indoor air quality. He is the Chief Science Officer of Indoor Science, a company he started in 2004. He speaks around the world on air quality topics and is a training provider of the Indoor Air Quality Association. Mr. Cull is a Licensed Professional Engineer (PE) and Certified Industrial Hygienist (CIH). His degree is in Environmental Engineering from the University of Illinois - Urbana Champaign. Mr. Cull has developed 50 air quality related courses for the IAQA University and is the author of the book, “Fundamentals of Mold Remediation”. In his words… “Besides being passionate about indoor air quality, I enjoy cycling, music, the Chicago Bulls, and having fun with my three kids.”