Promoting inter-regional water-carbon synergy is critical for sustainable development in water-scarce areas, where water use generates substantial CO2 emissions. This study quantitatively analyzes the water-carbon coupling relationship in water-scarce Gansu Province, China, aiming to improve water utilization efficiency (WUE) and carbon emission efficiency (CEE). We constructed a water-carbon stability index based on water-use carbon emission structure, using the projection pursuit model (PPM) and super-efficiency slacks-based measure (Super-SBM) to evaluate WUE and CEE, respectively, calculated coupling coordination via a coordination degree model, and analyzed the structural characteristics of Gansu's water-carbon correlation network using an improved gravity model, social network analysis (SNA), and block model. Key findings include: (1) both WUE and CEE showed fluctuating growth from 2013 to 2023 with more significant improvement in CEE; (2) water-carbon development exhibits mutual promotion and spatial coordination; (3) the coupling network has gradually tightened with enhanced connections and obvious spatial spillover effects; (4) inter-regional collaboration behaviors exist with block distributions closely tied to natural endowments. Consistent with local resource distribution and policies, these findings provide a scientific basis for water-carbon synergy in arid regions, with theoretical and practical significance.Research highlightsThe ability to maintain the water-carbon relationship is measured through the Gibbs-Martin index.The water carbon coupling coordination relationship is quantified in water-scarce areas.The spatial correlation of water conservation and carbon reduction is explored.