A recent review published in Engineering titled “Towards Sustainable Urban Water System: A Strategic Approach to Advance Decarbonizing Water Management” by Xinyu Pan, Yumeng Zhao and colleagues from the State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, and the State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, offers a comprehensive strategy for achieving sustainable urban water management through the integration of decentralized water systems (DWS), source separation, and low-carbon water treatment technologies.
The study highlights the critical role of urban water systems in global climate goals, emphasizing the need to reduce their carbon intensity. Traditional centralized water systems (CWS) are energy-intensive and contribute significantly to greenhouse gas emissions. The authors propose a paradigm shift from these linear, end-of-pipe treatment approaches to more sustainable, decentralized models that prioritize resource conservation and recovery.
DWS are identified as a fundamental component of sustainable urban water management. DWS advocate for treating small quantities of water as close to the source as possible, promoting circular models over traditional linear ones. The implementation of DWS involves considering social contexts, such as institutional frameworks, governance structures, and individual behaviors, alongside technical systems, including water management goals, spatial organization, and technology selection. The study notes that DWS can be more cost-effective than CWS, with internal and external costs potentially 40% and 35% lower, respectively. Additionally, DWS can reduce environmental impacts by up to 56% compared to CWS, particularly in the category of fossil resource scarcity.
Source separation is another key strategy discussed in the paper. By separating grey water, yellow water, and feces at the source, DWS can prevent cross-contamination and enhance resource recovery efficiency. Grey water, which has the highest volume and lowest pollutant content, can be treated and reused for non-potable purposes such as toilet flushing and irrigation. Urine, rich in nitrogen (N) and phosphorus (P), can be treated on-site to recover nutrients for fertilizer production. Feces, while containing lower levels of N and P, also represent a valuable resource for nutrient recovery through processes like composting and lactic acid fermentation. The study highlights that source separation systems can achieve a threefold reduction in carbon emissions compared to conventional systems, primarily due to increased biogas production and reduced N₂O emissions.
Low-carbon water treatment technologies are essential for achieving sustainable water systems. These technologies focus on resource conservation through rainwater control, efficiency improvements, and low energy consumption, as well as resource recovery through carbon capturing and energy/nutrient recovery. For instance, rainwater harvesting and green roofs can reduce dependence on centralized water supplies and lower energy consumption. Technologies like the anaerobic–anoxic–oxic membrane bioreactor (A²O-MBR) and facultative membrane bioreactor (FMBR) are highlighted for their efficiency in treating grey water and reducing sludge production. Additionally, microbial electrolytic carbon capture (MECC) and microbial electrosynthesis (MES) are presented as innovative methods for carbon capture and energy recovery.
The study concludes that integrating DWS, source separation, and low-carbon water treatment technologies offers a comprehensive and adaptable strategy for sustainable urban water management. This approach not only reduces carbon emissions but also promotes resource conservation and recovery, contributing to a more resilient and sustainable urban water system. Future research should focus on evaluating the environmental impact of pipelines in DWS, addressing emerging contaminants in drinking water sources, and assessing the broader applicability and user acceptance of low-carbon water treatment technologies.

The paper “Towards Sustainable Urban Water System: A Strategic Approach to Advance Decarbonizing Water Management,” is authored by Xinyu Pan, Yumeng Zhao, Xinlu Lin, Nianyi Zhao, Meng Sun, Jun Ma. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.03.028. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.