Tuesday, June 9, 2009

Risk of Legionella Bacteria in Rainwater

Information provided by Dr. Dennis Lye, an EPA Research Microbiologist

The causative agent of “Legionnaires Disease” is Legionella pneumophilia. This organism is ubiquitous in the environment. It can be found in ponds, pools of water, and even in eves/gutters of buildings. The mere presence of this organism is not enough to be a risk to humans. This is why most rainwater collections systems will not pose a risk to healthy humans.

However, we must be cautious and concerned when any of the following occurs:

  • The rainwater collection system is not treated and a biofilm build up within the system.
  • The water is heated at some point before usage.
  • The water is aerosolized in some manner (fountain, showerhead, mist, etc.) in a way that humans could be exposed to the aerosol.
  • Immunocompromised individuals (including infants and some elderly) coming into contact with any of these aforementioned water because they are more likely to be infected with this organism than a healthy individual.

Any of the following will help to eliminate concern about this risk:

  • Maintain a chlorine residual in the rainwater system.
  • Do not heat the water or aerosolize the water before usage.
  • Use the water for landscaping.

There is a Center for Disease Control (CDC) site with more information if you need it –