Unraveling chained optimization strategies for carbon emission control in WWTPs and effective water utilization within complicated water systems.

China faces severe water scarcity and significant greenhouse gas (GHG) emission pressures. As significant sources of GHG emission within urban system, wastewater treatment plants (WWTPs) exhibit a clear coupling relationship between wastewater treatment and urban water usage. However, the lack of trace of the water‑carbon nexus has created an obstacle to coordinating water utilization strategies and low-carbon wastewater treatment. In this context, the carbon emission intensity of the WWTPs and water use efficiency within the region were appropriately assessed focusing on the Yellow River Basin. A novel approach was introduced to analyze the chain of synergies between carbon neutrality and water conservation goals in urban water system. Specific chained optimization strategies tailored to each region were provided with dimensions linking different aspects of urban water system development, providing fresh perspectives and guidance for GHG mitigation, water resource utilization, and sustainable human development.