Legionella Management in Building Water Systems

ELI Policy Brief


This brief describes federal, state, and local policies that take a broad-based, primary prevention approach to controlling Legionella bacteria and other waterborne pathogens in building water systems by requiring the development and implementation of building water management plans. Key features of such plans include evaluating the risk to building occupants; identifying locations where Legionella could amplify within a building water system; and establishing a water management program to monitor and control Legionella growth and minimize potential exposures to the bacteria.

Background – Legionella and Indoor Air Quality

Legionella bacteria are the causative agents for two diseases that are known collectively as legionellosis – Legionnaires’ disease, a potentially fatal form of pneumonia, and Pontiac fever, a non-pneumonic illness characterized by flu-like symptoms. Legionella bacteria occur naturally in freshwater environments such as rivers, streams, and lakes. Legionella is an indoor air quality concern because the bacteria can and do get into building water systems. If not controlled, the bacteria can grow, multiply, and cause disease in susceptible people who inhale contaminated water mists or aerosols. Inhalation is the primary route of exposure; in general, the disease is not spread from person to person. U.S. Centers for Disease Control and Prevention (CDC), Legionella (Legionnaires’ Disease and Pontiac Fever); World Health Organization, Legionellosis.

According to CDC, the number of reported Legionnaires’ disease (LD) cases has been on the rise since 2000. Certain people are at greater risk of developing legionellosis: those over fifty years of age, current or former smokers, and those with certain health conditions. A 2016 study by CDC scientists reported that the fatality rate is approximately one in ten for community-acquired LD and approximately one in four for health care-associated cases.

Once Legionella bacteria begin to proliferate in building water distribution systems, they can colonize various parts of the system – e.g., piping, water storage tanks, water heaters, showerheads, faucet aerators, humidifiers, hot tubs, cooling towers and decorative water features. The key to reducing the risk posed by Legionella bacteria is to limit growth of the organism, which can be achieved through rigorous preventive maintenance of building water systems. The 2016 study noted above found that “[g]aps in maintenance that could be addressed with a water management program to prevent Legionnaires’ disease outbreaks were described in 23 (85%) of 27 investigated outbreaks.”

Preventive maintenance practices include maintaining proper water temperatures, pH and water chemistries; preventing water stagnation; and maintaining proper concentrations of water treatment chemicals such as rust inhibitors, anti-scaling agents, and biocides if necessary. See CDC, Developing a Water Management Program to Reduce Legionella Growth & Spread in Buildings.

Recent Industry Standards and Guidelines for Controlling Legionella in Building Water Systems

A notable development in advancing Legionella control policies and practices is the establishment of prominent industry standards and guidelines for managing building water systems to reduce Legionella growth. The following examples reflect the increasing attention to a prevention-oriented approach to managing Legionella risks. They are important in promoting best practices in buildings and in facilitating the development of federal, state and local policies that can help to institutionalize those practices.

ASHRAE Standard 188. One of the most widely quoted industry standards is ANSI/ASHRAE Standard 188, Legionellosis: Risk Management for Building Water Systems. The voluntary consensus standard – first developed in 2015 and revised in 2018 and 2021 – provides a framework for developing a water management program for building water systems. The standard outlines key components (“risk management principles”) that must be addressed in a water management program for building water systems. The standard also includes a number of preventive maintenance elements for potable water systems and for specified non-potable water systems, which must be incorporated in order to comply with the standard.  ASHRAE 188 does not require testing, but it does mandate periodic validation of program effectiveness, and a September 2021 addendum to the standard added a new appendix regarding minimum laboratory accreditation and documentation requirements, which apply when testing is part of the water management program. The standard applies to new and existing buildings and is designed for use in most building types except single-family homes. A related ASHRAE guidance, ASHRAE Guideline 12-2020: Managing the Risk of Legionellosis Associated with Building Water Systems, was updated in 2020 to provide direction on implementing ASHRAE 188. A longer summary of the ASHRAE 188 standard is provided here.

In 2016, CDC published a toolkit, Developing a Water Management Program to Reduce Legionella Growth & Spread in Buildings, which was updated in 2021. The toolkit supports the proactive approach described in the ASHRAE Standard and builds on its structure and content to provide guidance on developing and implementing a Legionella water management program. The toolkit uses accessible language, illustrations and examples to explain the key elements of a management program and may be used by building operators and owners without special training in engineering and building mechanical systems.

National Sanitation Foundation protocol. In 2017, the National Sanitation Foundation (NSF) released a Legionella protocol specifically for cooling towers. The purpose of NSF P453 (Cooling Towers – Treatment, Operation, and Maintenance to Prevent Legionnaires’ Disease) is to set forth “minimum practices required for treatment, operation, and maintenance of cooling tower water systems” to assist facilities in establishing a water management program. The protocol outlines proper maintenance and safety practices associated with evaporative cooling systems – hazard identification, control measures, monitoring, corrective action and validation. It also discusses routine and remedial treatment, as well as proper shutdown and start-up procedures during a planned or unplanned outage.

American Industrial Hygiene Association guideline. The American Industrial Hygiene Association (AIHA) has published a guideline titled Recognition, Evaluation, and Control of Legionella in Building Water Systems. The guideline promotes a proactive approach to minimizing Legionella amplification through source identification, risk assessment and control. Designed for trained professionals, the guideline “outlines the basic approaches to the development of evaluation and sampling strategies and the performance of post-remediation validation….” The guideline provides a framework for using Legionella sampling of building water systems to characterize amplification source hazards, identifying control measures and assessing their effectiveness in routine assessments. Unlike ASHRAE 188, the AIHA guideline provides specific recommendations on how and at what frequency to test Legionella concentrations. It also provides interpretive guidance for Legionella concentrations based upon the hazard posed by amplification with corresponding suggested actions that are based on currently available guidance and knowledge (though not on quantitative risk assessment). Because Legionella is not believed to pose a health risk unless it first amplifies within a water source, early identification and prevention of Legionella amplification is a major focus of the AIHA guideline.

Federal, State and Local Policies Requiring Water Management Plans and Programs to Control Legionella in Building Water Systems

Industry standards and technical guidelines help establish a “standard of care” and are an important impetus for changing building management practices. However, government policies also have a key role to play in ensuring that all building owners and managers follow best practices to prevent and address the conditions that lead to Legionella growth.

State and local governments might already have laws or regulations establishing general facility-related maintenance requirements for certain types of regulated facilities (e.g., healthcare, rental housing and other commercial properties), which could be applied to require action if a Legionella problem arises in those facilities. Similarly, the “general duty” clause of the federal Occupational Safety and Health Act requires employers to provide employees “a place of employment…free from recognized hazards that are causing or are likely to cause death or serious physical harm to workers,” and the clause may be enforced where a “workplace has a recognized, serious hazard for which there is no specific OSHA standard (e.g., occupational exposure to Legionella in water systems).” U.S. Occupational Safety and Health Administration, Legionellosis (Legionnaires' Disease and Pontiac Fever). In addition, some states have enacted policies that authorize public health agency actions in response to Legionella outbreaks.

A relatively small number of jurisdictions have policies that establish a primary prevention approach to Legionella control in building water systems. Following are summaries of selected federal, state, and local government policies that require the development, implementation and documentation of a water management plan and/or program for reducing Legionella risks. The policies vary in the types of facilities (e.g., health care-related) and/or water systems (e.g., cooling towers) covered, as well as the level of detail included in the policy provisions. 

This is not an exhaustive listing of policies that require water management programs or plans in the U.S., and the brief does not cover nonbinding guidance developed by state and local health agencies. The brief also does not address other types of regulation that can be important to controlling Legionella, such as building codes governing the design of premise plumbing systems and federal and state drinking water quality requirements.  

Federal Policy Examples:

State Policy Examples:

  • New York State: Two separate state health department regulations adopted in 2016. One requires owners of all cooling towers to have a maintenance program for each cooling tower, and to register, test, inspect and certify the cooling towers to prevent and reduce exposure to Legionella. The other requires all general hospitals and residential healthcare facilities to perform an environmental assessment of the facilities and adopt a Legionella culture sampling and water management plan.
  • Michigan: State health care licensing regulations require health facilities to implement a water management program based on ASHRAE Standard 188.
  • Virginia: 2020 law establishing Legionella prevention requirements for schools.
  • Illinois: Law and rules requiring certain facilities for Legionella and to have a water management plan.

Local Policy Examples:

  • New York City, N.Y.: 2015 city law (amended 2019) and implementing health department rules requiring owners of cooling towers in New York City to create a maintenance program and plan and to register, inspect, clean, disinfect and test their cooling towers.
  • New Orleans, La.: 2017 city ordinance adopting an amended version of the 2015 International Mechanical Code that includes a requirement for Legionella water management plans for cooling towers and other aerosol-producing equipment, and for corrective action in certain circumstances.

In addition, Ohio enacted a law in 2021 requiring the state director of health to adopt a hospital licensing rule that includes "standards and procedures for identifying monitoring, managing, reporting, and reducing exposures to risk conditions, such as Legionella, including through the use of environmental facility assessments, the development of water management plans, and the use of disinfection measures."

Some states and local governments have established laws or regulations that are narrower -- requiring specific practices or actions rather than the implementation of a water management plan. For example, the city of Garland, Texas adopted a provision in its Property Sanitation and Housing Services Code (City Code of Ordinances, §32.04(d)(6)) requiring owners of multifamily buildings and lodging establishments that use cooling towers to test the towers annually for Legionella. The testing must be conducted by a third party using city-approved procedures, and results must be submitted to the city. Massachusetts and California are examples of states with regulations governing the use of recycled or reclaimed water that expressly require cooling systems that create a mist to use drift eliminators and to treat the recirculating water with chlorine or another biocide to minimize the growth of Legionella and other microorganisms.  Colorado Water Quality Control Commission regulations (5 CCR1002-84) allow the use of reclaimed water indoors “provided that the user adopts and follows best management practices (BMPs) to minimize growth of and worker exposure to Legionella and other premise plumbing opportunistic pathogens,” and require a site-specific operation and maintenance plan that includes disinfection and monitoring BMPs as outlined in the regulation.


Policies last updated: March 2022

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