Urban Water Circularity Index: A Decision-Support Tool for Sustainable and Resilient Cities

Water circularity is increasingly recognised as a strategic component of sustainable urban management, yet robust municipal-scale assessment methods remain limited. This study introduces the Urban Water Circularity Index (UWCI), a composite indicator developed to evaluate water circularity in urban areas. Adapted from an existing circularity framework for industrial installations, the UWCI integrates 11 key factors covering water demand management, supply efficiency, reuse, wastewater treatment, drainage, diffuse pollution control, climate adaptation governance, green infrastructure, flood management, and institutional recognition. The methodology applies a knowledge-driven Multi-Criteria Decision Analysis approach, combining the Weighted Sum Model with expert-informed weights inspired by the Analytical Hierarchy Process. A conservative nonlinear scoring system places greater weight on the magnitude of sub-factor scores, preventing minor improvements from compensating for major structural weaknesses and reducing the risk of greenwashing. The UWCI ranges from −2.94 to +2.23 and is grouped into five circularity levels, from Critical/Highly Linear to Excellent/Fully Circular. The index was tested in eight municipalities: Dili (Timor-Leste), Rome (Italy), Cape Town (South Africa), Wellington (New Zealand), Loulé (Portugal), Lahti (Finland), São Paulo (Brazil) and Singapore. Scores were -1.83, -1.01, +0.08, +0.16, +0.16, +0.71, +1.41, and +1.89, allowing the distinction among different institutional, geographical, and infrastructural contexts. Singapore performed strongly due to integrated reuse, efficiency, governance, and green infrastructure. Dili’s low score reflects a capital in a world’s youngest and lowest-income countries, with limited infrastructure. Overall, the UWCI offers a transparent and policy-relevant tool for benchmarking urban water circularity, identifying weaknesses, prioritising investments, and supporting resilient urban water transitions.