Sustainability assessment of urban water and wastewater infrastructures, especially when it comes to managing existing systems, is of paramount importance. Hence, this study presents a comprehensive approach to investigate the sustainability of a real wastewater system under different water demand management policies (WDMPs) in the operation and maintenance stage. In this regard, life cycle sustainability assessment (LCSA) is used through its three main pillars, which are (1) environment, (2) economy, and (3) society. Accordingly, (1) Environmental assessment is conducted using life cycle assessment (LCA) considering a thorough inventory dataset; (2) The economic assessment results are analyzed by the life cycle cost (LCC) method; and (3) Social life cycle assessment (SLCA) is conducted using the analytic hierarchy process (AHP) method, in which three main stakeholders “public and local community”, “workers and employees”, and “treated wastewater and sludge consumers” are considered. Finally, to prioritize scenarios, the results of LCA, LCC, and SLCA for every scenario are aggregated to account for the sustainability score using the AHP. The results of applying the proposed method to a real case study show that scenarios leading to less reduction in wastewater production are more sustainable options as they represent better performance regarding economic and social aspects. The proposed framework provides a better insight into the integrated sustainability analysis of urban water infrastructures. In addition, it can be used as a guideline for exploring the effects of WDMPs on wastewater systems in different study areas.