Service Quality Index (SQI): a multicriteria approach for assessing water supply in Brazil

In water supply systems, performance indicators are essential for evaluating efficiency, efficacy, and effectiveness across the entire process, from collection to distribution. To assess the quality of water supply services through a single measure, this study proposes the Service Quality Index (SQI), a synthetic indicator designed to evaluate water supply services across Brazilian municipalities using data from the National Sanitation Information System (SNIS). The SQI integrates multiple operational indicators through a structured multi-criteria approach, with weights assigned via the Analytic Hierarchy Process (AHP). This type of comprehensive and methodologically index, designed to be self-sufficient for service quality assessment, represents a novel contribution in the Brazilian context. To evaluate the robustness of the index, Monte Carlo simulations were conducted, generating 100 random weight distributions for each indicator and comparing the resulting SQI values with those from the original formulation (SQI-A). These simulations demonstrated the index's stability under varying weight configurations. The SQI enables the classification of services into five quality categories, from excellent to very poor, and was applied to 4,654 municipalities, which also represents an unprecedented scale for studies with a similar purpose. Results show that 25.03% were rated excellent and 49.35% good, offering a comprehensive and replicable framework for performance benchmarking and policy planning in the water sector.