Water, a substance essential to life on Earth, has been submitted to various types of aggressions that can be characterized as pollution, and ultimately promote changes in its quantity and quality. Thus, the rivers in general need to be monitored, and monitoring constitutes itself as an important tool, especially for springs used for public supply. This paper studies the water quality of water sources used for public supply in the mountain region of Macae, Rio de Janeiro, Brazil, applying the Water Quality Index - WQI, to determine the efficiency of treatment processes employed and to verify the occurrence of environmental injustice (association of health risks and poverty). For achieving this purpose, water analysis was performed monthly in Simplified Watee Treatment Units located in three Macaé Municipality rural districts, namely Óleo, Bicuda Grande and Frade, during a semester. Data about financial income of the local population were also collected. Water quality data were treated by principal component analysis – PCA, and the calculated WQI is presented through graphs and tables; After analyzing the data, it is noticed that although the local water sources are of good quality, quality of distribution water is still a problem to be solved, and that an expressive parcel of the population lives on less than two minimum Brazilian national salaries, a fact that combined to health risks associated with environmental sanitation problems configures the occurrence of environmental injustice in the studies locations.

Keywords: water quality monitoring, water quality index - WQI, water treatment systems, Macáe’s mountain region, environmental injustice.