How to Minimize the Risk of Legionnaires’ Disease, According to the CDC

Written by: Hilary Nardone, Lead Environmental Group Manager

The Centers for Disease Control and Prevention (CDC) recently published data that showed reported Legionnaires’ disease cases are escalating. Furthermore, data taken during August and September showed 31% of all United States reported cases were in New York State.[1] The increase of cases in New York may be due in part to two factors: aging drinking water infrastructure and increased testing of patients as a result of recent city and state regulations.

Legionnaires’ disease is a pneumonia caused by inhaling or aspirating small water droplets containing Legionella bacteria. Legionella bacteria grow particularly well in man-made water systems, including building drinking water systems.

Image by: Janice Haney Carr via CDC

What does CDC recommend to minimize the risk of Legionnaires’ disease? 

  • CDC and other organizations endorse implementing a Water Management Program to reduce risk of disease. A complete Water Management Program will identify specific water system maintenance steps the building can take to combat the growth of Legionella bacteria.
  • When looking to control Legionella bacteria in a drinking water system, disinfectants work most effectively in the following pH range [2]
    • The anti-microbial efficacy of free chlorine declines as pH increases >7, with significant loss of efficacy at pH >8
    • The optimum pH range for formation of monochloramine is 7.5 to 9
    • Most drinking water systems have a pH of ≥7.5

If you are considering taking steps in your building to decrease growth and spread of Legionella bacteria, contact us today. Barclay Water Management’s Environmental Group produces Water Management Programs that comply with the ANSI/ASHRAE Standard 188-2018, Legionellosis: Risk Management for Building Water Systems. Our team also specializes in testing services for Legionella bacteria in potable and non-potable water systems and provides iChlor® monochloramine monitoring and control solutions.

[1] Centers for Disease Control and Prevention. National Notifiable Diseases Surveillance System, 2016 Annual Tables, 2017 Weekly tables, and 2018 Weekly Tables of Infectious Disease Data. Atlanta, GA. CDC Division of Health Informatics and Surveillance, 2017 and 2018. Accessed Oct 8, 2018. Available at:


[2] Centers for Disease Control and Prevention. Legionella (Legionnaires’ Disease and Pontiac Fever) Guidance for Monitoring Building Water. Accessed Nov 20, 2018. Last updated Oct 23, 2018. Available at:

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