Legionella Management in Building Water Systems

Developments in State Policy


Summary of ASHRAE Standard 188


The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) has created a voluntary consensus standard, ANSI/ASHRAE Standard 188, Legionellosis: Risk Management for Building Water Systems. First published in 2015 and updated in 2018 and 2021, ASHRAE 188 provides “minimum legionellosis risk management requirements for the design, construction, commissioning, operation, maintenance, repair, replacement, and expansion of new and existing buildings and their associated (potable and non-potable) water systems and components.” (Sec. 2.1.) The standard is designed for use in most building types except single-family residential homes. 

ASHRAE 188 requires building managers to survey the building for water system components that can aerosolize Legionella-contaminated water and for legionellosis-related factors, including building size and occupant health risk. Buildings that include specified non-potable building water systems (cooling towers, spas, fountains, etc.) must develop a water management plan for those systems. If the building has any of the legionellosis risk factors enumerated in the standard, the plan must address potable water systems as well. ASHRAE 188 lays out the general framework for the management plan; building owners and managers determine the detailed measures within that framework that will be followed. Section 6.2 outlines the required components of the management plan:

  • a designated program team;
  • a description of the potable and non-potable building water systems, including process flow diagrams, and an analysis of where hazardous conditions may exist in the systems;
  • the control measures (defined in Section 3 as “a disinfectant, heating, cooling, filtering, flushing, or other means, methods, or procedures used to maintain the physical or chemical conditions of water to within control limits”) to be used to limit Legionella growth, including locations of controls and control limits for chemical or physical parameters;
  • monitoring;
  • corrective actions;
  • program verification and validation; and
  • documentation and communication.

Under Section 6/2/8, building managers are to determine whether testing for Legionella must be performed and, if so, the testing approach and how test results will be used to validate the program. Section 7 includes additional specific requirements for potable and non-potable water systems, and Section 8 sets requirements relating to building construction, renovation, refurbishment, replacement or repurposing. An annex to the standard addresses requirements for healthcare facility water management plans.

The 2021 revision to the standard included amendments that “replaced permissive language with enforceable language [to] facilitate adoption of the standard for code and regulatory purposes.” An addendum to the 2021 edition created a new Appendix B to address minimum laboratory accreditation and documentation requirements, which apply when testing is part of the water management program.  

ASHRAE 188 is complemented by ASHRAE 12: Managing the Risk of Legionellosis Associated with Building Water Systems, a guideline first published in 2000 that was updated in 2020 to provide direction on implementing ASHRAE 188-2018.


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