The best water treatment products in the world won't make up for poor application and control. There are some very real water treatment challenges in buildings such as unrealistic cost expectations, a lack of commitment of manpower, and inadequate training of operating personnel. Good control can be achieved, however, if the owner and water treatment chemical vendor understand their individual responsibilities for program selection, control and priorities. This is a large subject and could cover a variety of systems. This paper will focus primarily on open recirculating cooling systems (cooling tower) and closed cooling/heating systems.