Potable water is becoming day by day more difficult and more expensive to obtain. Therefore to reduce the pressure in natural
water resources, wastewater reclamation is expanding through many municipalities and industries for applications where potable
water is not required. However, specific treatments must be performed before the water reuse. These treatments are necessary to
reduce physical-chemical and microbiological contaminants. This work has evaluated the action of chlorine dioxide (ClO2) and
sodium hypochlorite (NaOCl) in reducing the mesophilic aerobic micro-organisms population as well as diminishing the chlorine
demand in the water used. The results have shown that chlorine dioxide is less affected by water contaminants when compared to
sodium hypochlorite; a 3 log cycle reduction in mesophilic aerobic micro-organism population was obtained by using a ClO2
residual concentration of 0.2 mg∙L-1 and a chlorine residual, from NaOCl, of 0.8 mg∙L-1. To obtain these concentrations, it is
necessary to dose 5.0 mg∙L-1 of ClO2 and 15.5 mg∙L-1 of NaOCl in water.