Water treatment is a mystery to many consulting engineers, but is required for many reasons. In HVAC systems the most common goals of water treatment are to maintain peak performance, reduce water consumption and minimize corrosion, scale, and fouling while controlling microbial growth. This column summarizes the most important items for the HVAC designer to know and improve their master specifications for water treatment. © 2022 Amer. Soc. Heating, Ref. Air-Conditoning Eng. Inc.. All rights reserved.