The water treatment of open cooling systems with recirculation is based on the operation of concentration cycles, with corrosion inhibitors and deposits preventers only with complement. This technology does not consider the presence of soluble chemical species which lead to problems to the stability indexes. This was studied in an experimental design in an open water recirculation treatment system with an evaporative condenser of a chemical industry. It were collected samples of the reposition

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... nd recalculating waster at different levels of concentration, by changing the purging system. The parameters analyzed were pH, partial and total alkalinity, calcium roughness, chloride, conductivity, and also experiments with a corrosion proof. The results obtained in real operation conditions showed that the concentration of bicarbonate ion changes in a different way, when compared with the soluble ions as chloride. If the traditional treatment was used several stability indexes must be considered along the system and not a unique index, capable to establish all treatment process. It is presented that must be considered that the quality of the reposition water have to present specific conditions, as a previous treatment. Great care must be taken to use the water reuse in these systems, as an usual practice nowadays. The clean technology in these systems have limited use and must be revised, because can lead to conditions adverse to this technology, using greater quantities of chemical products.