How Does Legionella Get Into My Building?

  • 7 April 2020
  • Author: Dominick Tuzzo
  • Number of views: 4653

Whether your building is newly constructed or even 100+ years old, chances are, sooner or later, it can become colonized with opportunistic premise plumbing pathogens (OPPP’s) such as Legionella. 

As facultative intracellular pathogens, meaning they are capable of living either inside or outside of other host cells, Legionella enters your building water system(s) as an endosymbiont of another organism.  Translated:  they hitch a ride into your building inside of amoeboid cells which, incidentally, function as their natural host organisms in the aquatic environment.

“But we receive our domestic water from the City of (Your City Here), which always meets or exceeds the requirements of the Safe Drinking Water Act (SDWA) / National Primary Drinking Water Regulations.  How can host organisms harboring Legionella be entering my building?”

While the SDWA is designed to protect us from gastrointestinal disturbances and diseases from unsafe levels of Cryptosporidium, Giardia lamblia, E. Coli, and Coliforms, as well as the adverse health effects of metals, chemical contaminants, pesticides, and radionuclides, unfortunately for us, the Environmental Protection Agency (EPA) has not established any limits on Legionella.  While the SDWA provides us with water which is generally safe to drink, it does not however, give us water which is safe to breathe.

The EPA National Primary Drinking Water Regulations[1] state that:

  • Legionella: No limit, but EPA believes that if Giardia and viruses are removed/inactivated, according to the treatment techniques in the Surface Water Treatment Rule, Legionella will also be controlled.
  • Heterotrophic Plate Count (HPC): No more than 500 bacterial colonies per milliliter.

The water entering your building is not sterile.  While most bacteria entering is harmless, we need to recognize that statistically speaking, there is a lot of it entering your premise plumbing, and some if it may contain opportunistic human pathogens.  The EPA permissible level of HPC’s allows up to 500 bacterial colonies per milliliter (500 cfu/mL) of heterotrophic bacteria to enter your respective buildings and into our domestic water manmade plumbing systems.  What does this mean for you?  Let’s do the math to discover the precise implications:

There are 3,785 mL in a single gallon of water.

The EPA permits up to 500 cfu of bacteria in each mL of drinking water.

500 cfu/mL X 3,785 mL = up to 1,892,500 cfu heterotrophic bacterial cells to exist within each and every single gallon of water entering our buildings.

1.89 million X number of gallons our buildings use per day = billions of bacterial cells, some even harboring OPPP’s, to enter our buildings each and every day.

From a risk management (likelihood of exposure) perspective, the odds are:

  • Getting struck by lightning

=        1 in 700,000

  • Dying in a plane crash 

=        1 in 5,000,000

  • Winning the Lottery 

=        1 in 300,000,000

  • Bacteria entering our building water 

=        >1,000,000,000 to 1





For assistance in controlling your buildings waterborne pathogen risks, Water Management Plans, Sampling Plans, Risk Assessments, accredited third-party lab sampling, audits, supplemental and emergency disinfections, consultations, or any questions, contact your Chem-Aqua Water Risk Management Service Group today at:


Written by: Dominick Tuzzo


(Environmental Protection Agency, 2020)

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