Design, operation and treatment of cooling systems can encompass many techniques to fulfill both the desires of Industry and Management to improve its environmental image. Environmental impact reaches much further than the “greenness” of a given cooling water treatment chemical in the discharge from a cooling system. When assessed in depth, “traditional” chemicals or treatments may be “greener” than conventionally imagined or portrayed. Non-Chemical Devices (NCDs) have great appeal when talking of the impact of treatment chemicals. “Marketing” of some treatment chemicals emphasizes their “biodegradability”. Some aspects of “environmental impact” of various approaches to the design, operation and treatment of open evaporative cooling systems are discussed.