The current worldwide water resources issue is one of the crucial matters to overcome obstacles to sustainable development. This problem, formerly tackled in a sectored manner, is now pointing towards an analysis directed to treating the watershed as a management unit, with regards to all dimensions of knowledge and, especially, to the public participation in the decision-making processes. As an alternative to measure its performance, it has been sought out to develop indexes aimed to measure its sustainability, but there is still a lack of the use of composed efficient methodologies that also enable public participation in decision-making. This research presents a methodology comprising 15 indexes for the calculation of the Watershed Sustainability Index (WSI), followed by the application of the PROMETHEE multi-criteria analysis method and the COPELAND multi-decision-maker method. The methodology was applied to evaluate the performance of subwatersheds of the Piranhas-Açu watershed, located in the Brazilian northeast semi-arid region. The performance ordering, obtained through the application of the methods, emphasizes that subwatersheds' performances are uneven. It can be noticed that the subwatersheds' performances are still far from ideal in relation to water resources management, even in the ones that displayed satisfactory index levels.