In this type of recirculation cooling method, the water to be cooled is introduced to the pond and cooled gradually by natural evaporation, radiation and convection. Large ponds were needed to meet normal cooling demands because cooling is accomplished very slowly and requires the impoundment of large amounts of water. A typical 1000 mw steam electric power plant, for example, may have required a 2000-acre cooling pond. Since cooling ponds dissipate approximately 55% of the added heat by evaporation, they consume less water than cooling towers, which reject more than 80% of the added heat by evaporation.

Slowdown from cooling ponds is comprised of bottom seepage and controlled overflow to the source stream. Because of the large rainfall receiving surface areas, concentration ratios are typically quite low, up to about 1.5 times source concentration. But even such low concentration increases may be significant in terms of reduced CaC03 solubilities, so condenser tubes on pond systems are more likely to scale than they are on once-through cooling systems. Sulfuric acid may be fed to maintain pH below saturation values (pHs). Scale inhibitors and dispersants are sometimes required in conjunction with acid feed for complete scale prevention.

A significant aspect of cooling ponds is that they promote "homes" for a variety of aquatic organisms. They often support large fish populations. Specific bio-dispersants, in conjunction with periodic feed of chlorine, may be needed to keep condenser tubes free of biological slimes initiated by the microorganisms of the food chain supported by the pond.