With significant efforts made to consider water reuse in cities, a robust and replicable framework is needed to quantify the degree of urban water circularity and its impacts from a systems perspective. A quantitative urban water circularity framework can benchmark the progress and compare the impacts of water circularity policies across cities. In that pursuit, we bring together concepts of resource circularity and material flow analysis (MFA) to develop a demand- and discharge-driven water circularity assessment framework for cities. The framework integrates anthropogenic water flow data based on the water demand in an urban system and treated wastewater discharge for primary water demand substitution. Leveraging the water mass balance, we apply the framework in evaluating the state of water circularity in Singapore from 2015 to 2019. Overall, water circularity has been steadily increasing, with 24.9% of total water demand fulfilled by secondary flows in 2019, potentially reaching 39.6% at maximum water recycling capacity. Finally, we discuss the wider implications of water circularity assessments for energy, the environment, and urban water infrastructure and policy. Overall, this study provides a quantitative tool to assess the scale of water circularity within engineered urban water infrastructure and its application to develop macro-level water systems planning and policy insights.

在考虑城市中水再利用方面做出了巨大努力，需要一个强大且可复制的框架来从系统的角度量化城市水循环的程度及其影响。一个定量的城市水循环框架可以衡量城市间水循环政策的进展并比较其影响。为此，我们将资源循环和物质流分析 (MFA) 的概念结合起来，为城市开发一个需求和排放驱动的水循环评估框架。该框架整合了基于城市系统用水需求的人为水流量数据和处理过的废水排放，以替代主要用水需求。利用水质量平衡，我们应用该框架来评估新加坡 2015 年至 2019 年的水循环状况。总体而言，水循环量一直在稳步提高，2019 年二次流满足了总用水量的 24.9%，在最大水循环能力下可能达到 39.6%。最后，我们讨论了水循环评估对能源、环境和城市水基础设施和政策的更广泛影响。总体而言，本研究提供了一种量化工具来评估工程城市水基础设施内的水循环规模及其在制定宏观水系统规划和政策见解方面的应用。以及城市供水基础设施和政策。总体而言，本研究提供了一种量化工具来评估工程城市水基础设施内的水循环规模及其在制定宏观水系统规划和政策见解方面的应用。以及城市供水基础设施和政策。总体而言，本研究提供了一种量化工具来评估工程城市水基础设施内的水循环规模及其在制定宏观水系统规划和政策见解方面的应用。