Building water systems can present an ideal environment for the growth of bacteria, including Legionella bacteria, which causes Legionellosis (Legionnaires' Disease and Pontiac Fever). Legionella pneumophila is the primary bacterium in the Legionella genus that causes Legionellosis. You may be exposed if you breathe in water vapor containing Legionella bacteria.
The Centers for Disease Control and Prevention (CDC) monitors outbreaks of Legionnaires' Disease through two surveillance systems at the national level. According to their most recent data, reported cases of Legionnaires’ Disease have been increasing since the 2000s, peaking in 2018. Cases dropped slightly during the COVID-19 pandemic but have since started to rise again. Incidence rates continue to be higher in the Northeast and Midwest regions of the U.S. and in the summer and fall months. Hotels, assisted living communities, and nursing homes have been most susceptible to recent outbreaks.
As technology becomes more common in buildings – and our building systems become more connected and smarter – we can tap into that technology as a tool in our approach to water safety. Traditional detection and prevention methods can now be supplemented with tools like AI-driven monitoring, predictive analytics, and automated water management systems. These technological tools are just beginning to transform how we identify and mitigate Legionella risks in complex water systems such as those in hospitals, hotels, and commercial facilities. These tools will continue to evolve and assist us in staying ahead of the curve to protect the public’s health.
A recent study originally published in Water Research and then described in MedBound Times (February 22, 2025) illustrates how AI-driven water monitoring may be a cost-effective solution to the early identification of Legionella risk factors. In this case, machine learning models were used to predict Legionella risks in a large New York healthcare facility. By integrating real-time water quality data collection throughout the buildings’ plumbing system, including pH, temperature, chlorine concentration, electrical conductivity, and oxidation-reduction potential, the research team was able to detect risk zones and implement early interventions, including targeted flushing. Implementing these technologies will likely accelerate over the coming months.
The CDC identified contributing factors in 23 of the outbreaks from 2000 to 2014. Approximately 65% were due to process failures, such as not having a building water system management program (Garrison LE, 2016, p. 579). With this in mind, the source for Legionnaires cases is much more likely to be from a buildings' drinking water system, where exposure points such as water fountains, sinks, ice machines, and showers are common. Therefore, having a Building Water System Management Plan is necessary to prevent Legionella from occurring within the building water system.
The CDC issued a guidance document to assist facilities in developing water management programs to reduce Legionella growth entitled "Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings: A Practical Guide to Implementing Industry Standards."
CHA Consulting, Inc. (CHA) uses CDC resources, as well as the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard 188-2021, entitled "Legionellosis: Risk Management for Building Water Systems," and ASHRAE Standard 12-2023, entitled "Managing the Risk of Legionellosis Associated with Building Water Systems," to develop Building Water System Management Plans. ASHRAE Standard 188-2021 provides minimum components to include in a plan, and 12-2023 describes how to develop an effective water management plan.
CHA's process includes reviewing the building's domestic water piping system to develop a flow diagram and to understand the system thoroughly. Water system measurements are then collected for chlorine residual, pH, temperature, and turbidity. The condition of the current water treatment systems is then reviewed and evaluated. A CDC Legionella Environmental Assessment Form (EAF) is then completed for each building to identify plumbing features and areas of risk. CHA uses this information to develop a Building Water System Management Plan, which includes:
Legionella remedial options include ultraviolet treatment, superheating, and hyper-halogenation. However, CHA recommends system flushing as a new remedial approach and the preferred remedial option in our plans. There is a risk of exposure to unsafe temperatures and high chlorine levels with two of the common remedies. Further, flushing is a significantly cheaper alternative compared to ultraviolet treatment, superheating, and hyper-halogenation options. Flushing procedures allow clean chlorinated water from the municipal water supply to reach the entire system. Our method is based on a study published in Applied and Environmental Microbiology that found that 0.5 ppm total chlorine will eliminate 99% of Legionella pneumophila within approximately five minutes (Kuchta, 1983, p. 1136). CHA has successfully used this option at several client locations.
Regular system flushing is an easy process to implement and maintain and will reduce the potential for bacteria growth. CHA recommends flushing if a water system has been unused (stagnant) for two or more weeks and can provide training to facility maintenance staff during initial flushing activities so the facilities themselves can manage future flushing activities and reduce costs.
CHA recommends that all building owners develop a Building Water System Management Plan to reduce the potential for Legionella bacteria in their building water system. According to the Environmental Protection Agency Office of Water, Legionellosis cases have been most frequently linked to a potable water supply, cooling towers, or components of water distribution systems.
CHA's flushing remedy is more cost-effective than installing and maintaining costly ultraviolet or hyper-halogenation systems and is more cost-effective to maintain than superheating. It is also much safer to implement than the three other options. Once the plan is developed and training is provided to maintenance staff, it could be managed internally to reduce cost if desired.
It is essential to have a Building Water System Management Plan to prevent Legionella growth and protect building occupants. By maintaining a long-term water management program and reviewing your plan annually, you will effectively manage and maintain your building profile, which will help you mitigate risk and prevent the spread of Legionella in your building water systems. In the future, we expect technology to play a larger role in mitigating risks.