Legionella Management in Building Water Systems

Developments in State Policy



  • Background – Legionella and Indoor Air Quality
  • Scope of this Policy Brief
  • Recent Industry Standards and Guidelines for Controlling Legionella in Building Water Systems
  • Federal, State and Local Policies Requiring Building Water Management Plans and Programs
  • Other Policy Strategies Not Covered in this Policy Brief

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; the agency saw a more than four-fold increase in reported cases from 2000 to 2016. CDC, Legionella: History, Burden, and Trends. Some LD cases are associated with outbreaks, while many are individual cases. CDC, Vital Signs: Deficiencies in Environmental Control Identified in Outbreaks of Legionnaires’ Disease — North America, 2000–2014. Certain people are at greater risk of developing legionellosis: those over fifty years of age, current or former smokers, those with chronic lung disease, those who are immunosuppressed and those with underlying illnesses like diabetes, kidney or liver disease. CDC, Legionella: Causes, How it Spreads, and People at Increased Risk. CDC has reported that the fatality rate is approximately one in ten for community-acquired LD and approximately one in four for health care-associated cases. CDC, Vital Signs.

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. A CDC review of 27 Legionnaires’ disease outbreaks 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.” CDC, Vital Signs.

Preventive maintenance practices, which may differ for different water systems and features, 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. CDC, Developing a Water Management Program to Reduce Legionella Growth & Spread in Buildings.


Scope of this Policy Brief

Policy development addressing Legionella bacteria in building water systems has gained momentum in recent years, following a notable shift in public health recommendations published in 2015. This policy brief focuses on government policies that take a broad-based, primary prevention approach to Legionella control 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.

The main purpose of this brief is to track and describe federal, state and local policies that establish requirements for water management plans and programs to control Legionella and other waterborne pathogens. The brief does not discuss nonbinding government policies, such as guidance developed by state and local health agencies. See, e.g., Allegheny County (PA) Health Department, Updated Guidelines for the Control of Legionella in Western Pennsylvania (1997, rev. 2014); see also 2017 Illinois House Resolution No. 94 (encouraging the state to provide schools guidance on developing and implementing comprehensive water quality management plans). Nor does it cover well-established regulatory strategies adopted by other countries and cities outside the U.S. – e.g., Australia, New Zealand, the United Kingdom.

Before describing governmental policies, it is helpful to note recently-established voluntary consensus standards and guidelines for managing Legionella risks.


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

A notable development in advancing Legionella control policies and practices is the recent establishment of prominent industry standards and guidelines for managing building water systems to reduce Legionella growth. The following examples of documents published in just the past few years 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. Perhaps the most widely quoted industry standard developed in recent years is ANSI/ASHRAE Standard 188, Legionellosis: Risk Management for Building Water Systems. The voluntary consensus standard – first developed by the American Society of Heating, Refrigerating and Air Conditioning Engineers 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 valildation of program effectiveness, and a September 2021 addendum to the standard added a new appendix regarding minimum laboratory accredditation 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.

Because a number of government policies reference ASHRAE 188, a longer summary of the 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. Also in 2015, the American Industrial Hygiene Association (AIHA) published a new 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.

However, only a 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 establish such an approach. The policies all require the development, implementation and documentation of a water management plan and/or program for reducing Legionella risks. Those adopted following publication of ASHRAE Standard 188 reference the standard, but do so in different ways. The policies also 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.

The policies described below do not represent the only possible regulatory approaches to requiring water management plans. This brief will be updated as new policies are adopted by other state and local jurisdictions.

Click the links for detailed summaries of the policies.



  • 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


  • 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 to the above policies, in 2021, the Ohio legislature enacted a law requiring the state director of health to adopt hospital licensing rule that include "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."

Virginia enacted a law (Va. Code § 22.1-138) that includes a short provision on Legionella management in schools. Effective July 2021, each school board in the state must “maintain a water management program for the prevention of Legionnaires' disease at each public school building in the local school division.”  The law further requires school boards to “validate each water management program on at least an annual basis to maintain the health and decency of such buildings” and to maintain and make available for review files related to the water management program, including the results of all validation and remediation activities.  As required in the legislation enacting the new law, the Virginia Department of Education issued "recommendations for the establishment, maintenance, and validation of water management programs to prevent Legionella pneumophilia growth in public school buildings in 2021; those recommendations include a statement that "all Virginia school boards and their school building maintenance operations (or an outside accredited Legionella testing laboratory consultant) shall comply with ASHRAE 188-2018."

Some states and local governments have established laws or regulations that are narrower, requiring specific practices or actions rather than the implementation of a 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. The state of Illinois enacted a law in 2021 (210 Il. Stat. 45/3-206.06, 210 Il. Stat. 85/6.29) that requires hospitals and nursing homes to develop a policy for testing their water supply for Legionella bacteria, including the frequency of testing, and to make the policy and test results available to the Department of Public Health on request. In 2022, the Department of Public Health adopted regulations requiring such policies to be based on specified ASHRAE and CDC publications and to include, at a minimum, a procedure to conduct a facility risk assessment to identify potential Legionella and other waterborne pathogens in the facility water system; a water management program that identifies specific testing protocols and acceptable ranges for control measures; and a system to document the results of testing and corrective actions taken. (77 Il. Admin. Code 250.1100 (hospitals); 77 Il. Admin. Code 340.1337 (veterans' homes), 77 Il. Admin. Code 330.792 (sheltered care facilities).)

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.


Other Policy Strategies not Covered in this Brief

While implementing water management plans and programs for the proper operation and maintenance of building water systems are a key component of a primary prevention approach to Legionella control, other areas of policy not covered in this brief are also important.

Drinking Water Regulation. Drinking water quality requirements help ensure that water is properly treated before it enters a building. The federal Safe Drinking Water Act (SDWA) authorizes the U.S. Environmental Protection Agency (EPA) to establish health-based standards for public water systems to protect users from potentially harmful contaminants. EPA drinking water regulations do not establish a maximum contaminant limit for Legionella, but they set a maximum contaminant limit goal of zero. Among other things, the regulations require treatment techniques (e.g., disinfection, filtration) to remove and/or inactivate Giardia and viruses, and these measures are expected to control Legionella as well. States implement the SDWA through their own laws and regulations, which may include requirements that are more stringent than federal standards. One issue raised in recent years is that if a healthcare or other facility serving 25 or more users adds supplemental disinfectants to its potable water system, this “secondary treatment” might convert the facility into a public water system subject to SDWA (and related state) regulation.

Premise Plumbing System Design. Another area of regulation, new construction/renovation codes governing the design of premise plumbing systems (the portion of the system from the water meter to the tap), can help prevent Legionella growth by addressing issues such as temperature, pipe sizing, dead legs and mixing valves. States and/or local governments can incorporate best practices for premise plumbing system design through their building and plumbing codes and through other laws that set requirements for new construction and renovation of various types of buildings. A related issue is whether water conservation policies that result in lower flow increase the risk of Legionella growth; in 2017, EPA awarded two research grants to study water quality issues and health risks related to low-flow conditions of drinking water in premise plumbing systems.


Watch for updates to this page as new policies are adopted.

Rev. April 2021

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