Gives details of advice contained in ASHRAE Guideline 12 issued in May 2000. States it provides environmental and operational guidance that will contribute to the safe operation of building water systems to minimize the risk of legionnaires' disease. It is intended for use with non-residential building systems and centralized systems in multi-family residential buildings. Some of the advice is also applicable to single family residential buildings. States the Guideline is suitable for use by designers, installers, owners, operators, users, maintenance personnel and equipment manufacturers.