Water scarcity is a major challenge to global sustainable development. Reclaimed water with ecological applications is a key solution to enhance the water supply security and water environment safety in urban areas. At the same time, it is also a key source of greenhouse gas emissions in urban water system. Therefore, the development of reclaimed water system needs to consider both environmental and climate benefits under the constraint of ecological safety. However, it is not clear what are the system-wide environmental benefits including pollutant and greenhouse gas mitigation and ecosystem service value realization. There also lacks a system optimization methodology to optimize the reclaimed water system under ecological safety constraints. Lastly the pathways towards a safe and low-carbon reclaimed water system are not obvious for various regions with distinct local characteristics. To address these knowledge gaps, this project plans to develop methods to evaluate ecosystem service values, optimize the system design under ecological safety constraints, and identify localized low-carbon system development pathways. The outcomes of this project are expected to provide decision support for developing an ecologically safe and low-carbon reclaimed water system with beneficial ecological applications.