The river basin is a complex environmental system, resulting from the interrelationships between the physical-natural and socio-economic subsystems. Identifying it as a unifying unit for environmental processes and human interference has led to its adoption as a research unit, allowing for the assessment of environmental quality and sustainability, based on the analysis of physical-chemical, biological and socio-economic factors. The aim of this work is to compose a Water Use Sustainability Index (ISA) to help support the adoption of public policies aimed at the sustainable use of water resources.