The open recirculating system is perhaps the most commonly encountered cooling system in the industry. These units are basically open to the atmosphere, where heat is expelled through the process of evaporation. Evaporation and the cooling effect it brings lowers the temperature of the bulk water, which circulates through various types of heat exchange equipment, picks up heat and returns to the "open" tower to repeat the cycle.

It is essential to maintain clean surfaces for an effective cooling water treatment program. The selection of an effective program involves many complex issues, including the operating characteristics of the system, the water chemistry and the severity of problems encountered, prior to the selection of a trouble-free scale, corrosion, foiuling and microbiological inhibition program.