ABSTRACT: Pharmaceuticals are considered to be important environmental contaminants. The aim of this study was to evaluate their presence in water intended for public supply to Municipally of Rio de Janeiro, Brazil. The regional environmental assessment was done from the analysis of surface water and distribution for the presence of psychiatric drugs. The study reveals the presence of benzodiazepine derivatives in all samples of surface water samples of the Guandu River, with the amounts of 42ng L - 1, 198 ng L - 1 and 335 ng L - 1 for bromazepam, clonazepam and diazepam, respectively. The population served by Companhia Estadual de Águas e Esgotos (CEDAE) is the order of ten million. Psychiatric pharmaceuticals, in particular, are thought to impose significant ecological risks. A better understanding of the real impact of these pollutants implies a comprehensive evaluation of their persistence and fate in environmental matrices. The studies presented in this article are intended to contribute to improve the knowledge about the occurrence of some psychiatric drugs in the water supply.