Aerosolized water: Small droplets of water in the air (generally, 5 microns in diameter or less), which can contain Legionella or other bacteria and can be deeply inhaled into the lungs

Biocide: See disinfectant

Biofilm: Germs and the slime they secrete that stick to and grow on any continually moist surface; provides a stable growth surface and an environment with nutrients for many types of germs, including Legionella

Building water systems: Includes hot and cold water distribution systems and all devices that use water to which people can be exposed, such as hot tubs, decorative fountains, and cooling towers

Control: To manage conditions within the building according to a water management program or to maintain established criteria

Control limits: Maximum value, minimum value, or range of values acceptable for the control measures being monitored to reduce risk for Legionella growth and spread

Control measures: Actions that can be taken for building water systems to limit growth and spread of Legionella, such as heating, adding disinfectant, or cleaning; control measures enable maintenance of control limits

Control points: Locations in water systems where a control measure can be applied

Corrective action: Actions taken to reestablish control when monitoring values or measurements are outside control limits

Dead legs: Piping subject to low or no flow because of design or decreased water use; for example, capped pipes or unused faucets

Disinfectant: Chemical or physical treatment to kill germs; for example, chlorine, monochloramine, chlorine dioxide, bromine compounds, copper-silver ionization, ultraviolet light, or ozone

Disinfectant residual: Amount of disinfectant available in water to kill bacteria

Drift: Water mist or small droplets carried by air, which may include aerosols

Hazardous conditions: Any condition or factor that can contribute to the growth and spread of Legionella to a person if not controlled

Healthcare facility: Hospitals, long-term care facilities, clinics, or other settings where patients seek care, such as dental offices, pharmacies, or outpatient laboratories

Legionella: Bacteria that can cause Legionnaires’ disease

Legionnaires’ disease: A serious type of pneumonia caused by Legionella

Make-up water: Water provided to a device to replace system water lost through evaporation, processing, or draining

Non-potable water: Water not intended for people to drink or ingest, such as water for industrial processes, irrigation, or equipment like cooling towers

Non-routine Legionella testing: Testing for Legionella to investigate potential sources of environmental exposure for persons with disease. Testing for public health investigations should always be performed in conjunction with the public health authority having jurisdiction

People at increased risk for Legionnaires’ disease: Includes people 50 years or older, current or former smokers, people with a chronic lung disease (like emphysema), people with weak immune systems or who take drugs that weaken the immune system, people with cancer, and people with underlying illnesses such as diabetes, kidney failure, or liver failure

Potable water: Hot or cold water intended for people to drink or ingest, such as drinking, bathing, food preparation, and dishwashing

Remediation: Response activities taken to reduce contamination in response to control measures, such as routine Legionella test results, that persistently exceed control limits or to events that pose an immediate risk to control of building water systems; required whenever Legionnaires’ disease occurs; may also be appropriate for unexpected events such as equipment failure or acts of nature that disrupt the water system

Residual: See Disinfectant residual

Routine Legionella testing: Testing for Legionella to establish a baseline measurement for performance indicators or for validating a water management program or corrective action. Methods and objectives vary from those of non-routine Legionella testing

Sediment and scale: Mineral build-up in a water system that uses up disinfectant and supports growth or survival of bacteria

Stagnation: When water does not flow well; areas of stagnation encourage biofilm growth, ambient temperatures, and disinfectant residual reduction

Supplemental disinfection: Adding disinfectant to a water system on site; may require permitting for potable water systems

Validation: Activities to confirm the water management program is working as intended and is effective for Legionella control; testing for Legionella is one method for validation of a water management program

Verification: Activities to confirm the water management program procedures are occurring as intended; reviewing temperature logs to ensure temperature measurement is occurring at the intended frequency is one method for verification of a water management program

Water age: Amount of time it takes for water to reach a point of use or fixture/device from the point of entry; for example, slow moving water has a higher water age than water moving quickly through a building water system

Water management program (WMP): Multistep process to reduce Legionella growth and spread; includes establishing a team, describing building water systems, identifying areas or devices where Legionella might grow or spread to people, determining control measures, monitoring control measures, establishing remediation activities and interventions when control measures are not met, ensuring the program is running as designed and is effective, and documenting all program activities

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