NAS – Management of Legionella in Water Systems - Legionella

NAS – Management of Legionella in Water Systems

Management of Legionella in Water Systems.
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The Water Science and Technology Board – The National Academies of Sciences, Engineering, and Medicine.

Stronger Policies Needed to Protect the Public From Legionnaires’ Disease – NAS News August 14 2019 .

More uniform protection of public health is needed from Legionella in building water systems, including hospitals and healthcare facilities, and cooling towers across the country, the report says. It calls for a range of actions to combat the growth of the bacteria, including the following:

For all types of buildings, hot-water heater temperatures should be maintained above 140°F (60°C) and the hot-water temperature to distal points (the point of connection to a fixture such as a faucet, showerhead, or thermal mixing valve that blends hot and cold water right before they reach the tap) should exceed 131°F (55°C). Maintaining water temperature outside Legionella’s preferred growth range is the main Legionella control strategy, and it has been proved successful by multiple field studies. These temperature requirements could be codified by changing building and plumbing codes for residences and other buildings or by modifying the Centers for Medicare and Medicaid Services (CMS) memo that affects health care facilities.

Guidance is needed for homeowners about practical steps that can be taken to combat Legionella bacteria. For example, flushing stagnant water from taps after periods of disuse may help to prevent Legionella. Increasing the water temperature in household hot-water heaters to 140°F (60°C) also can help limit Legionella growth in home hot-water systems, but this step must be weighed individually against the risk of scalding and burns.

All public buildings such as hotels, businesses, schools, apartments, and government buildings should be required to have a water management plan. ASHRAE 188, AIHA (2015), and other guidance documents are available to help create a water management plan that can meet this requirement. Ideally, this requirement would be codified by either local jurisdictions with authority (such as building inspectors) or state authorities (such as departments of environmental protection or health). Once codified, this requirement could be enforced by insurance companies; i.e., without a water management plan, a building would not qualify for insurance.

Low-flow fixtures should not be allowed in hospitals and long-term care facilities, due to these buildings’ high-risk occupant populations. Low-flow fixtures have been promoted to conserve water and sometimes energy, but these fixtures increase water stagnation and reduce disinfectant levels, presenting a greater risk for Legionella.

Criteria for certifying green buildings, energy-conserving features, and water conservation features should be modified to take into account risk factors for growth of Legionella in building water systems. Green buildings have exacerbated problems with Legionella by lowering hot-water temperatures and by lengthening the amount of time water sits in pipes, which leads to a decrease in disinfectant and associated biofilm growth. Substantial water conservation can still be potentially achieved while protecting public health if the water is more deliberately managed to prevent stagnation – for example, through routine flushing of a target fraction of the water use.

Cooling towers should be registered and monitored. Building- and industrial-scale cooling towers – which remove heat from recirculating water used in water-cooled chillers, heat pumps, and other HVAC equipment — have been implicated in many outbreaks of Legionnaires’ disease. These towers may generate bacteria-laden aerosols that drift away from the facility and then are inhaled by people working and living in the building or by passersby. Cooling tower registries allow for rapid public health response to community clusters of Legionella cases, including timely remediation of sources of infection.

A minimum disinfectant level should be required throughout public water systems, along with monitoring for Legionella. EPA should require a minimum level of disinfectant in public water systems and validate that the treatment is working by routine monitoring for Legionella. Monitoring could focus on warm-water conditions and be triggered when water temperatures consistently exceed 20°C.

In addition, education about how to monitor, prevent, and control Legionella is needed for those designing water systems, overseeing municipal water supplies, developing and implementing plumbing codes, as well as for those in government responsible for the safety of buildings, cooling towers, and water supply. And well-funded studies in multiple jurisdictions are needed to determine the most common sources of sporadic Legionnaires’ disease, which is critical to reducing the rising rates observed over the last 20 years.

The study — undertaken by the Committee on Management of Legionella in Water Systems was sponsored by the Centers for Disease Control and Prevention, U.S. Department of Veterans Affairs, U.S. Environmental Protection Agency, and the Alfred P. Sloan Foundation. The National Academies are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. They operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln. For more information, visit  

Sara Frueh, Senior Media Officer.
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