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Legionella - Building Environmental Prevention

Building owners can take steps to prevent the growth of Legionella in water distribution systems and heating/cooling/ventilation systems, and cooling towers through the development and use of water management plans, use of environmental controls and monitoring, and development of remediation or treatment plans if Legionella is detected.  

High Risk Facilities

Certain types of building and facilities are at higher risk for the growth of Legionella.  High risk facilities are those that house sensitive populations, have large complicated water systems, are more than 10 stories, and have cooling towers.  The Centers for Disease Control and Prevention (CDC) recently identified that common settings for Legionella outbreaks include hotels, long-term care facilities and hospitals.  The CDC has developed a worksheet to identify buildings at increased risk for Legionella growth and spread.  The CDC has also developed a legionnaire prevention quick reference guide for surveyors 

Water Management Plans

The purpose of development and use of a water management plan, also called water safety plans, is to prevent Legionella growth, and to have a plan for remediation in case of an outbreak.  The components of a water management plan include:

  • Establish a water management program team
  • Describe the building water systems using text and flow diagrams
  • Identify areas where Legionella could grow and spread
  • Decide where control measures should be applied and how to monitor them
  • Establish ways to intervene when control limits are not met
  • Make sure the program is running as designed and is effective
  • Document and communicate all the activities 


Water Management Plan Resources

ASHRAE (2015). Standard 188-2015, Legionellosis: Risk Management for Building Water Systems. American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., Atlanta, Ga.

CDC (2016). Developing a Water Management Program to Reduce Legionella Growth & Spread in Buildings. Centers for Disease Control and Prevention.

What Owners and Managers of Buildings and Healthcare Facilities Need to Know about Legionella Water Management Program

Considerations When Working with Legionella Consultants


Environmental Assessments


Facility managers should conduct an environmental assessment of the facility identifying and documenting the areas of concern within the facility. Environmental assessments provide a complete understanding of a facility water system and helps identify areas of risk.  These assessments can be used to help identify areas to implement environmental monitoring for temperature or chlorine residuals (CDC resource on chlorine residual testing), or sampling for Legionella if needed.  CDC has developed a tool kit for conducting environmental facility assessments which can be accessed at:

Understanding factors that lead to Legionella growth will help facility managers successfully conduct an environmental assessment.

Proactive Environmental Monitoring

Based on the results of the environmental assessment, routine monitoring of parameters such as chlorine residual and temperature may be useful to provide measurable standards for ensuring that system is not conducive to Legionella growth.   Proactive monitoring of temperature and chlorine should record the fixture location, the initial temperature and chlorine residual, the maximum temperature and chlorine residual, as well as the time it took to reach each maximum (follow this link to see an example of a record sheet).  Proactive monitoring should include decision points on action levels with a corresponding plan of action when unacceptable levels are present. 

CDC has developed a sampling data sheet for use with environmental monitoring or data collection:

It is recommended that a CDC ELITE certified laboratory be used for any sample analysis for Legionella.  Here is a link to CDC ELITE certified laboratories:

Long-Term Control

An environmental assessment of the facility or the water management plan may identify risk factors that merit use of long term control measures for the water distribution system or HVAC system to prevent or reduce Legionella growth.   Common long-term control measures for hot water distribution systems include, temperature control (maintaining temperatures above 120 degrees F), continuous disinfection of the water system including chlorine, monochloramine, chlorine-dioxide, copper-silver ionization, ultraviolet radiation, and point of use/entry filtration. Control points include measurable factors that contribute to Legionella growth, like temperature, disinfectant residual level, and flow rate.  Some of these treatment systems may require a licensure as a public water system with Ohio EPA, contact the Division of Drinking and Groundwaters to learn more.

Long-term control measures for cooling towers and HVAC systems with exposed water sources need to ensure proper maintenance and physical cleaning of the tower or system as per the manufacturer’s recommendations to prevent Legionella growth.

Updated 5/30/2018