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Water System Management for the Prevention of Legionnaires Disease & ANSI / ASHRAE Standard 188

According to the CDC (Centers for Disease Control) between 8,000 and 18,000 cases of Legionnaires Disease are reported annually with over 10% of the cases fatal. Both Legionnaires Disease and the less-severe influenza-like Pontiac Fever are the result of exposure to Legionella bacteria, usually associated with building water systems.

ASHRAE LogoThe presence of Legionella bacteria alone is not sufficient to cause the disease. Additional environmental conditions that promote Legionella growth as well as a means of transmitting the disease via aerosol generation must also be present. ANSI/ASHRAE Standard 188-2015 provides minimum requirements for both potable and non-potable water systems and components in commercial buildings. Secondary disinfection methods such injection of chlorine (Cl2), chlorine dioxide (CLO2) or Miox MOS (mixed oxidant solution) should be considered as part of the solution. Successful prevention of the growth of Legionella requires a diligent water management program including the points outlined in ANSI/ASHRAE Standard 188-2015.

Specific requirements in the standard include:

  • Minimum Legionellosis risk management requirements for buildings and their associated potable and non-potable water systems.
  • Establishment by building owners of a Program Team and (in turn) a Water Management Program for which they are responsible in order to comply with the standard.
  • Provision of specific and detailed requirements for what Legionellosis control strategies must accomplish and how they are to be documented – but, does not provide (or place restrictions on) what specific strategies are to be used or applied.

The following is an outline of the steps in a comprehensive water management program as detailed in Standard 188.

  1. The first step in a comprehensive water management program is to identify the individuals responsible for program implementation and management. Once the water management team is identified and in place, schematics of the water systems (both potable and non-potable) and flow diagrams should be created.
  2. Next, an analysis of the water systems including evaluations of the points where hazardous conditions may occur need to be identified. Once these points are identified, control measures can be applied. It’s important that the control measures not only be applied, but also be regularly maintained to stay within established control limits. This requires an ongoing monitoring of both the physical and chemical characteristics of the water system.
  3. Ongoing monitoring includes established procedures to determine whether control measures are operating within established limits. If control measures are deemed to not be operating within the established limits, then corrective action should be taken within required response time.
  4. The next step in a successful water management program is to determine that established procedures are being implemented as designed (verification) and are effectively controlling the hazardous conditions throughout the water system (validation). Validation may include testing for Legionella and the detailed testing process.
  5. The final step in the water management program is the thorough documentation and communication of activities in the program. At minimum, a master document providing the location of all program documents should be maintained.

Standard 188 consists of normative sections followed by normative and informative appendices. The normative sections and normative appendices specify the requirements to comply. The informative appendices and informative references are provided for guidance.

Long term Legionella prevention is only possible with diligent water system program management. Routine monitoring and testing of the effectiveness of program control measures can provide early warning of potential problems, such as the presence of Legionella bacteria. With our aging population and new medications that suppress immune systems, more people are susceptible to infection each year. When Legionella preventive measures are effectively implemented, Legionnaires Disease prevention is possible.

For detailed ANSI/ASHRAE Standard 188-2015 information, visit

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