Our future is urban. With more than two-thirds of the global population expected to live in cities by 2050, urban sustainability is an essential part of sustainable development but remains poorly understood for urban agglomerations, which continue to develop and grow. Here, we construct a multiregional input-output table at the city level and investigate the impacts of water and carbon flows on the intercity supply chain of the Beijing-Tianjin-Hebei agglomeration in 2012. Our analysis reveals an economic-environmental imbalance whereby Beijing and Tianjin prosper at the expense of Hebei cities. Hebei cities work as producers for Beijing and Tianjin, such that services and goods exported from the Hebei region account for more than 60% of the region's carbon emissions and water use. Economic benefits are also exported. In the case of five key Hebei cities, only 38% of the region's gross domestic product is retained within the cities. This disparity has important implications for equality, prosperity, and sustainability and demonstrates the importance of considering supply chains from the city networks perspective.