The study has the objective to characterize indicators of environmental quality of water of mountainous areas with different impacts, defining and quantifying the environment benefits of the forested ecosystems. This work was accomplished in the municipal district of Nova Friburgo mountainous area of the State of Rio de Janeiro, in two basins with distinct land uses, that contributes for the watershed of the Paraíba do Sul river.The sub-basin of Rio Grande that possesses 22,000ha, suffers impact of the agriculture of high productivity. The watershed of Debossan river with 1,000ha, it possesses 100% of its covering with forest in advanced apprenticeship of regeneration. The Station of Treatment of Water of Rio Grande needs 1300m2 of built area, 12 employees and a considerable demand of chemical products (floculan, whitewash and chlorine), reaching a medium productivity of 263.15 l/s. The Station of Treatment of Water of Debossan needs 100m2 of built area, 3 employees and just the use of the chlorine in the treatment of the water to reach a productivity of 192.94 l/s. The data of quality of water of Rio Grande were supplied in periods of two hours with four year-old duration (2000, 2001, 2002 and 2003), while the consumption of chemical products for the station's it was daily. The results of the regression analysis indicated that the chemical products are effective as indicators of the environmental quality of the source, classifying them for the proposal of OECD as indicators of State for its simple use and as indicators of Pressure, when analyzed through historical series. The floculan links with the production of sediments of the watershed, the whitewash to the impact of the agriculture through the use of agricultural input and the chlorine to the urbanization. The indicator better fitting was the chlorine, explaining 97.76% of the variation of the parameters of quality of the water, being followed by the floculan and for the whitewash, that they explained 97.01% and 90.08%, respectively. The ecosystem watershed of Rio Grande is reaching a new homeostatic balance when observed the environmental functions (rainy periods), and he comes with degradation tendency when observed the antropic impact in the dry periods. Such impact happens by virtue of the disordered agricultural and urban development, being in degradation process for the same reasons. The tendency of degradation of Rio Grande or increase in the cost of its production it was on the average of 8.88% a year and in the four years of 26.46%. In the case of the sub-basin of Rio Grande it still counted with its referring environmental hydrologic functions and its antropic impacts mitigated, the economy for the four years of the study could be U$141,394.75.
