Decoupling wastewater-related greenhouse gas emissions and water stress alleviation across 300 cities in China is challenging yet plausible by 2030

Urban wastewater treatment and reuse infrastructure play a vital role in achieving water sustainability; however, the pathways to realize water–climate synergies in planning such infrastructure are not clear. Here we examine the nexus of urban water stress and greenhouse gas (GHG) emissions resulting from expanding wastewater infrastructures across over 300 cities in China. We find that, despite a total increase of 176% in life-cycle GHG emissions, larger-scale wastewater treatment and reclaimed water reuse have nearly tripled the average amount of urban water stress alleviated between 2006 and 2015. However, with an extensive and integrated application of existing low-carbon technologies for wastewater treatment, sludge disposal and water reuse, it is possible to substantially further decouple water stress mitigation from GHG emissions by 2030. Under the optimized scenario, China can reduce wastewater-related emissions by 27% at the national level, while its eastern and northern cities could reduce emissions by over 40% for every unit of alleviated water stress. This study provides insights into the water–climate nexus and outlines feasible pathways to reduce water stress while mitigating wastewater-related GHG emissions. The rapid urbanization in China calls for an expansion of urban wastewater treatment systems, which in turn may exacerbate climate impacts. With an extensive and integrated application of existing low-carbon technologies for wastewater treatment, sludge disposal and water reuse, it is possible to substantially decouple urban water stress mitigation from greenhouse gas emissions.