This presentation covers the background and history of legionellosis and the conditions in building water systems that amplify it. The key parts of ANSI/ASHRAE Standard 188-2015 are summarized to give the audience a conceptual framework and sources of more in depth knowledge are given. Compliance requirements, health care facility requirements, the necessary building survey to assess the risk of LD, the key elements of a WMP (water management plan), control points, and the verification and validation requirements. The design, documentation, operation & maintenance of building water systems by the program team of knowledgeable persons is stressed.