This column discusses proposed ANSI/ASHRAE Standard 188P, Prevention of Legionellosis Associated with Building Water Systems, which requires a Legionella hazard analysis and critical control point (HACCP) water plan for hospitals, nursing homes, office and apartment buildings, hotels, and other buildings with 10 or more stories, centralized water heaters, or an incoming water supply with a chlorine concentration of less than 0.5 ppm. The standard, which is expected to be released later this year, will also require HACCP principles in the maintenance of cooling towers, whirlpool spas, ornamental fountains, misters, air washers, and humidifiers.