Potable Water Legionella & Microbiology Testing

Are Legionnaires’ Disease Bacteria Lurking in Your Potable Water System? 

Potable Water Legionella & Microbiology TestingA major source of Legionella bacteria proliferation resulting in an increased risk of Legionnaires Disease (LD) is the premise potable water system.  The temperatures found in building water systems along with areas of low usage, or stagnation can allow for the development of biofilms. These biofilms provide for amoeba and help to protect Legionella, thus encouraging the proliferation of the bacteria.  Building occupants can then become exposed to these infectious bacteria via aerosolization through use of the water fixtures such as faucets and showers.  A susceptible individual, especially those in hospitals and nursing homes could contract LD from this exposure. 

To prevent your building’s water system from becoming a health risk, the Centers for Disease Control and Prevention (CDC) recommends that building owners and managers implement a Water Management Program (WMP) in accordance with ANSI/ASHRAE Guideline 188-2021 (ASHRAE 188).  This code ready guideline calls for certain facilities to develop a program team that will evaluate their plumbing systems for risk and develop controls to limit those risks.  These controls must then be verified and validated to show that they are controlling for Legionella proliferation.  The best method of validation is environmental sampling for Legionella in your facility.  EST can guide you through implementing a validation plan that satisfies your WMP.


Potable Water Legionella Testing 

Dr. Richard Miller and the EST Team have been providing expert Legionella testing, interpretations, and recommendations since the early 1980’s.  These valuable tools have allowed our customers to provide a safe environment for their building’s occupants.  We have the experience and credentials to help you protect your facility, staff, occupants, and visitors from Legionella bacteria. 

Below is some information from The CDC regarding Potable Water Systems and Water Management.


Understanding potable water system design components is critical for Legionella control. The following considerations apply to hot and cold potable water systems. They should be evaluated from the point at which water enters a facility system to the point where it leaves the system through a fixture or device.

Design Recommendations

  • Use pipe insulation to maintain hot and cold water temperatures throughout the water system.
  • Eliminate sections of no- or low-water flow called dead legs.
  • Install thermostatic mixing valves as close as possible to fixtures to prevent scalding while permitting circulating hot water temperatures above 120°F (49°C).
  • Recognize that low-flow and mechanically complex fixtures (e.g., electronic sensor faucets) can increase the risk of Legionella growth.
  • Identify water system components that speed the decay of disinfectant residuals (e.g., UV devices, water softeners, carbon filters, heaters).
  • Use appropriately sized hot and cold water storage tanks fitted with recirculating pumps to maintain flow and avoid unfavorable temperature gradients.
  • Consider installing sampling ports throughout your water system in locations to facilitate water parameter monitoring and WMP validation. 

What does the CDC recommend for Legionella Control?

Operation, Maintenance, and Control Limits

Use a WMP to protect building operators, staff, and visitors from exposure to Legionella in potable water systems. No single measure can ensure Legionella control. A comprehensive WMP allows water system operators to layer a series of complementary control measures to create environmental conditions that prevent bacterial intrusion, growth, and transmission. Develop or refine a WMP with the following guidelines in mind:

  • Monitor temperature, disinfectant residuals, and pH frequently based on the performance of the water management program or Legionella performance indicators for control. Adjust measurement frequency according to the stability of performance indicator values. For example, the measurement frequency should be increased if there is a high degree of measurement variability.
  • Store hot water at temperatures above 140°F (60°C) and ensure hot water in circulation does not fall below 120°F (49°C). Recirculate hot water continuously, if possible.
  • Store and circulate cold water at temperatures below the favorable range for Legionella (77–113°F, 25–45°C); Legionella may grow at temperatures as low as 68°F (20°C).
  • Ensure a disinfectant residual is detectable throughout the potable water system.
  • Flush low-flow piping runs and dead legs at least weekly and flush infrequently used fixtures (e.g., eye wash stations, emergency showers) regularly as needed to maintain water quality parameters within control limits.
  • Clean and maintain water system components, such as thermostatic mixing valves, aerators, showerheads, hoses, filters, and storage tanks, regularly.
  • Do not presume supplemental disinfection systems will control Legionella without an adequate WMP.
    • Selecting or operating a supplemental disinfection system inappropriately may result in system damage or health hazards (e.g., disinfectant byproducts). Consult with a water treatment professional regarding supplemental disinfection systems. They may require permitting.
  • Recognize that point-of-use (POU) microbial filters with an effective pore size of 0.2-microns or less that comply with the requirements of ASTM F838 can provide immediate control at individual fixtures in a water system if integrated into a WMP.
    • POU filters protect only the connected fixture. Correct location selection is critical to Legionella exposure prevention across the water system.
    • Follow the manufacturer’s recommendations regarding the frequency of replacement and appropriate operating conditions.
    • POU filters may need to be removed before performing an acute remediation procedure.
  • Consider testing for Legionella in accordance with the routine testing module of this toolkit.

What do I do in case of an outbreak?

If an outbreak or illness is suspected, test in conjunction with public health in order to:

  • Confirm the presence of Legionella before performing remediation.
  • Confirm elimination of Legionella after remediation activities.

If control measures are ineffective, if routine results indicate poor Legionella control, or if an outbreak or illness is suspected by the authority having jurisdiction (AHJ), consider the remediation options described below. Note: The public health AHJ determines whether there are associated illness(es) or an outbreak. Choose a remedial treatment procedure after considering the system infrastructure, water quality parameters, and available sampling results. Consult with a water treatment professional as certain procedures should only be undertaken by a professional. Following a successful Legionella remediation procedure, recolonization of the water system is likely unless the underlying conditions supporting Legionella growth are addressed.

  • Chemical shock using an elevated level of a disinfectant, such as chlorine, for a limited duration can control Legionella in a potable water system. Consult scientific evidence and technical expertise before choosing a specific chemical shock procedure. In addition:
    • Consider which components of the water system need remediation.
    • Chemical shock of a hot water system may have improved efficacy if the temperature is lowered.
    • Chemical shock options may be impacted by regulations (e.g., chemicals allowed into sewer discharge) and may require permitting.
  • Thermal shock of water systems is not recommended as the sole method of remediation due to rapid recolonization of Legionella.  

Read the full guidance at the CDC website. 


What can Dr. Legionella and the EST Team do to help?  

Potable Water Legionella Testing 

  • Analyses that measure Legionella control:

    • Legionella pneumophila serogroup 1– Primary Legionnaires disease pathogen should be None Detected or < 0.1 cfu/ml (colony forming units per milliliter). EST recommends QUARTERLY testing unless otherwise directed by your Water Management Program.
    • Legionella pneumophila serogroups 2-14 –Important Legionnaires disease pathogen should be < 1 cfu/ml. EST recommends QUARTERLY testing unless otherwise directed by your Water Management Program.
    • Legionella (other species)– Important Legionnaires disease pathogenshould be < 1 cfu/ml. EST recommends QUARTERLY testing unless otherwise directed by your Water Management Program.

Potable Water Legionella – Interpretations and Recommendations

Learn more about which testing method would be best for Legionella Control in your potable water system here:

Potable Water Legionella

Developing a Water Management Program 

The development of a WMP in accordance with ANSI/ASHRAE Guideline 188-2021 is critical for those facilities that qualify.  Buildings that have the following systems onsite or meet the following requirements are instructed to develop a WMP to reduce the risk of Legionnaires Disease.

  • Cooling Towers and/or Evaporative Condensers
  • Whirlpool Spas
  • Ornamental/Decorative Fountains
  • Air Washers, Humidifiers, or Misters
  • Any other device(s) that release(s) aerosols
  • A centralized hot water system supplying multiple housing units.
  • More than 10 stories, this includes below grade levels.
  • Residents over the age of 65
  • Any area(s) housing or administering care to individuals with certain health factors. 

There are multiple tools to assist in developing these WMP either directly from ASHRAE 188, using the CDC Legionella Toolkit and through the use of a third party electronic software such as the LAMPS system through HC Info. EST can provide you with consultation on the industry best practices for WMPs and sit on your Water Management Team as an expert consultant.  Our Legionella results come with Interpretations and Recommendations that have been used by many of our clients as the basis of their mandated responses to validation failures or positive samples.

Learn more about LAMPS and the CDC Toolkit at the links below:




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