Life Cycle Sustainability Assessment of Urban Wastewater Reuse: Successes, Persistent Pitfalls, and a Practical Path Forward

Achieving sustainable urban water management is increasingly critical amid climate change, water scarcity, population growth, and intensifying pressure on freshwater resources. Life Cycle Sustainability Assessment (LCSA) has emerged as a promising integrated framework to evaluate the holistic sustainability of municipal wastewater reuse systems by combining environmental Life Cycle Assessment (LCA), Life Cycle Costing (LCC), and Social Life Cycle Assessment (S-LCA). This paper presents a critical narrative review synthesizing current evidence on LCSA applications specifically in urban municipal wastewater reuse contexts—encompassing non-potable urban, agricultural, and potable reuse—and identifying which configurations deliver genuine sustainability benefits, where major methodological shortcomings persist, and how the field can advance toward more robust, policy-relevant practice. The evidence base was assembled through structured searches in Scopus, Web of Science, and Google Scholar, screened from over 300 references to 25 peer-reviewed studies retained for in-depth analysis. Among the retained studies, positive outcomes were most often reported under low-carbon energy grids, short transport distances, and appropriate reuse-type matching: hybrid decentralized systems were associated with overall sustainability scores up to 4.8 times higher than conventional supply, while cluster-scale systems were associated with reductions in global warming potential of 15–40%. Persistent pitfalls include weak pillar integration, an underdeveloped social dimension, inconsistent system boundaries, and insufficient consideration of absolute sustainability. In response, this paper proposes the RENEW-LCSA Framework (Renewable Water-Oriented Life Cycle Sustainability Assessment Framework)—a practical six-step operational approach incorporating reuse-type-specific Social LCA indicators, explicit absolute sustainability assessment against the Water Scarcity Index (WSI) and local carbon budgets, and evidence-based integration of Nature-Based Solutions (NbSs). Three paradigmatic cases—Windhoek (Namibia), Singapore (NEWater), and Los Angeles County (USA)—illustrate the framework’s systematic application. By moving beyond optimistic narratives, this review advances the credibility of LCSA as a decision-support tool for safe, equitable, and circular urban water management, contributing to SDG 6 and the European Water Reuse Regulation (2020/741).