Legionella update for public water suppliers

This fact sheet discusses what water system operators need to know about guarding against Legionella.

Legionella is a risk factor at large facilities such as hospitals, hotels, and office buildings. It can cause forms of pneumonia known as Legionnaires' disease or Pontiac fever. Operators of drinking-water treatment plants need to know about risk factors and disinfection procedures to prevent Legionella outbreaks. 

Table of Contents

What is Legionella?

Legionella is a bacterium found naturally in freshwater environments at generally low levels, but can become a health problem when amplified in building water systems, especially large, complex water systems such as hotels, hospitals, and office buildings. When Legionella grows in the biofilm of plumbing and is aerosolized through devices such as showers, cooling towers, hot tubs, or fountains, people can breathe in small, contaminated water droplets. Inhalation of Legionella may result in a severe form of pneumonia known as Legionnaires’ disease, or in a milder form known as Pontiac fever.

What is Legionnaires' disease?

Legionnaires’ disease (LD) is a serious type of pneumonia (lung infection) caused by Legionella bacteria. People can get sick when they breathe in mist or accidentally swallow water into the lungs containing Legionella.
More information on Legionella can be found on the Centers for Disease Control website at: http://www.cdc.gov/legionella/index.html.

The common sites of Legionella transmission are:

  • Potable water systems used for showering
  • Cooling Towers Systems
  • Decorative fountains
  • Biofilm of the distribution system

Additional Resources

What environmental conditions favor the spread of Legionella?

One environmental condition that favors the spread of Legionella is a temperature range of 77°F to 130°F. This is the typical temperature range of hot-water systems, shower heads, and even cold-water systems in warm climates. The recommended energy-saving step of lowering hot-water-heater temperatures below 120°F will have the unintended consequence of favoring Legionella growth. Therefore, lowering the temperature below 120°F is not recommended. Legionella is dispersed through aerosols; it thrives in stagnant water conditions and heating and cooling systems that produce aerosols.

Where do Legionella outbreaks typically occur?

Legionella is the leading cause of waterborne disease outbreaks in the United States. Outbreaks can be severe, especially in susceptible populations, causing hospitalization and death. Outbreaks are commonly associated with buildings or structures that have complex water systems, like hotels and resorts; long-term care facilities; hospitals; and cruise ships. The most likely sources of infection include water used for showering, hot tubs, decorative fountains, and cooling towers (structures that contain water and a fan as part of centralized air-cooling systems for a building or industrial processes). Multiple outbreaks have been associated with health-care facilities, and because of the sensitive populations that reside there, health-care agencies have some of the most robust policies on Legionella control.

Additional Resources

Is Legionella included in MassDEP regulations?

Yes. For surface water sources only, Legionella is regulated under the Surface Water Treatment Rule (SWTR) as a Treatment Technique, 310 CMR 22.20, with a maximum contaminant level goal (a non-enforceable guideline) of zero Legionella organisms for drinking water and a treatment technique for Legionella control (e.g., filtration and maintenance of a detectable disinfectant residual). Therefore, no monitoring for Legionella is required since there is no Maximum Contaminant Level (MCL).

310 CMR 22.03(3) of the Massachusetts Drinking Water regulations states that facilities served by a public water system that meet criteria that might otherwise make them a consecutive water system do not need to be regulated by MassDEP if they meet five criteria, the first of which is that they do not treat the water. Facilities that install permanent or temporary treatment must comply with the Massachusetts Drinking Water Regulations.

What are Massachusetts Department of Public Health (MDPH) requirements for Legionella?

Legionellosis (another name for Legionnaire’s disease) is a notifiable disease in Massachusetts. Local boards of health (LBOH), healthcare providers, laboratories, and other public health personnel must report the occurrence of notifiable diseases as required by Massachusetts General Laws, Chapter 111, Sections 3, 6, 7, 109, 110, 111 and 112 and Chapter 111D, Section 6, to the Massachusetts Department of Public Health (MDPH). MDPH reviews all reported cases and works with the LBOH to determine if it is necessary to contact the local public water supplier and MassDEP.  Even though Legionella is primarily a premise plumbing issue, if MDPH and the LBOH determine that the local public water system needs to be evaluated, MassDEP and the public water system will be notified and MassDEP will work with all parties to resolve the issue.  

All Legionella health complaints or questions should be referred to the LBOH and MDPH. 

Additional Resources

How have the Centers for Medicare & Medicaid Services sought to control Legionella?

The US Department of Health & Human Services Centers for Medicare & Medicaid Services (CMS) issued a revised survey and certification letter on July 6, 2018, that outlines the expectations for healthcare facilities to have water-management policies and procedures to reduce the risk of growth and spread of Legionella and other opportunistic pathogens. The policy was also intended to provide general awareness on Legionella and other pathogens for all healthcare organizations. Facilities must have water-management plans and documentation that, at a minimum, ensure that each facility:

  • Conducts a facility risk assessment to identify where Legionella and other opportunistic waterborne pathogens (e.g., Pseudomonas, Acinetobacter, Burkholderia, Stenotrophomonas, nontuberculous mycobacteria, and fungi) could grow and spread in the facility's water system;
  • Develops and implements a water-management program that considers the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) industry standard and the CDC toolkit;
  • Specifies testing protocols and acceptable rangers for control measures, and documents the results of testing and corrective actions taken when control limits are not maintained;
  • Maintains compliance with other applicable federal, state, and local requirements.

Note: The CMS does not require water testing for Legionella or other opportunistic waterborne pathogens. Testing protocols are at the discretion of the provider.

Healthcare facilities are expected to comply with CMS requirements and conditions of participation to protect the health and safety of their patients. Those facilities unable to demonstrate measures to minimize the risk of LD are at the risk of citation for non-compliance.

Additional Resources

How has the US Veterans Health Administration sought to control Legionella in their facilities?

On August 31, 2014, the Veterans Health Administration issued a directive to its facilities for the prevention of healthcare-associated Legionella disease and scald injury from potable distribution systems. The Legionella prevention activities in the directive involve assessing risks, monitoring water quality and implementing commensurate engineering controls to limit the growth of Legionella. Use of engineering controls to limit Legionella growth include ongoing monitoring of implemented controls, validating that the control measures are effective at inhibiting Legionella growth, and modifying implementation or type(s), as necessary. The Directive focused on engineering controls to the overall microbiological quality of facility water, not just the inhibition of Legionella growth. The Directive further noted that Legionella growth in building potable water distribution systems is primarily suppressed by the implementation of engineering controls such as maintenance of appropriate water temperatures or biocide (e.g. residual oxidant) levels. Application of more than one control may be necessary for the successful inhibition of Legionella growth.

Additional Resources

If you are an operator of a drinking water treatment plant, what should you do?

  • Check the list of health care facilities to identify facilities that receive water from your water system.
  • Find out about the CMS and VHA Legionella compliance practices of these facilities in the course of your routine work (e.g., during cross-connection-control inspection)
    • For any of the facilities that are on your system you should determine if there are changes within these facilities that could impact your system programs (e.g., cross-connection control or emergency-response program), or that would require the facility to become a consecutive public water supplier and thus be regulated by MassDEP (e.g., treatment addition).
  • Refer to MassDEP any facilities that meet the definition of a public water system per 310 CMR 22.00 (e.g., the facility installs permanent or temporary treatment). Send referral by email to the MassDEP Drinking Water Program at program.director-dwp@mass.gov, subject: Potential PWS.
  • Any facility that serves 25 or more people, more than 60 days a year, that is receiving water from another public system and is considering adding treatment to the water served in the facility (e.g., hospital, hotel, casino, etc.), must comply with the Massachusetts Drinking Water Regulations, policies and guidelines. The chart and form below will assist the facilities described above to determine the​ steps to take when considering installing drinking water treatment.
  • Determine if you need to update any of your programs/plans (e.g., cross connection or emergency response) as a result of any new information about these facilities. Update programs/plans as needed.

Additional Resources

Other resources

Association of State Drinking Water Administrators
The Association of State Drinking Water Administrators developed a paper on what building/facility water-systems operators should know about the management of Legionella. The white paper highlights the issues surrounding building that install treatment and are then considered public water systems under the Safe Drinking Water Act (SDWA) and subject to SDWA requirements. “Reducing exposure and controlling Legionella…… In buildings where Legionella has grown in the premise plumbing, the water provided by the public water system is a likely initial source. There are currently efforts to conduct a study monitoring for Legionella in the water in the distribution systems of public water systems that will provide a better understanding of the occurrence of Legionella in a distribution system. Regardless of whether the public water system is the original source of the Legionella found in premise plumbing, water systems can support control of Legionella and other opportunistic pathogens by providing water with optimal disinfectant residuals to all customers.” For details, see:

American Water Works Association
Research on disinfection residuals and Legionella by Mark W. LeChevallier, "Occurrence of culturable Legionella pneumophila in drinking water distribution systems."
Please note: “The data suggest that, to prevent elevated concentrations of L. pneumophila, utilities should maintain at least a 0.1 mg/L in all parts of the distribution system.”

US Environmental Protection Agency
Information for consumers on Legionella
For water-system operators: technologies for Legionella control on premise plumbing systems

Centers for Disease Control

Massachusetts Department of Public Health

American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
Building water management plans can also reduce and control Legionella growth in building water systems. These plans include a description of the building water system, a team to develop and manage the plan, control measures, and monitoring to verify that the plan is working. The most recognized industry standard for building water systems management plans is ASHRAE 188.

NSF International
NSF International is also working on Standard NSF 444 for prevention of injury and disease associated with building water systems.

Association of State and Territorial Health Officials

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