[Spatiotemporal Patterns and Driving Mechanisms of Reclaimed Water Utilization in China]

Reclaimed water serves as a crucial strategy to alleviate global water scarcity and advance United Nations sustainable development goal (SDG) 6, offering an essential pathway toward the sustainable utilization of water resources. Despite growing recognition of reclaimed water (RW) as a sustainable solution to water scarcity, China has yet to systematically characterize its spatiotemporal evolution or fully understand the mechanisms driving its utilization. This study applies a combination of hierarchical cluster analysis (HCA), principal component analysis (PCA), and the seemingly unrelated regression (SUR) model to uncover national patterns and temporal trends in RW use. It also quantitatively examines the influence of natural, socioeconomic, and anthropogenic factors. The evolution of reclaimed water utilization in China can be categorized into three distinct phases: ① inefficient use during the national standards refinement period (2002-2008)； ② policy-target-driven expansion (2009-2016)； and ③ accelerated efficiency gains driven by synergistic effects of policy, market forces, and technological advancements (e.g., widespread adoption of membrane bioreactor (MBR) technology) from 2017 to 2023. These developments were shaped by four primary drivers: economic growth, water resource endowment, industrial policies, and agricultural infrastructure. Spatially, RW utilization rates exhibited a pattern of "regional divergence constrained by agricultural activities." Over time, the drivers of this spatial variation have shifted from being primarily influenced by top-down policy promotion to a combination of regional characteristics and policy alignment. In agriculturally dominant regions, inadequate rural infrastructure has severely limited sewage collection and treatment capacity, resulting in a paradoxical situation of high utilization rates but low absolute reuse volumes-highlighting the urgent need for distributed treatment systems. The inverse effects of water resource endowment on reclaimed water usage-in which utilization rates increase while usage volumes decrease during wet seasons and vice versa during dry seasons-underscores the strategic role of reclaimed water as a flexible regulatory resource. This characteristic positions RW as a critical component in adaptive water resource management, especially under changing climatic and demographic conditions. As constraints on freshwater resources intensify and demographic advantages wane, China's reclaimed water strategy must evolve from simple capacity expansion toward optimization and efficient allocation. This study provides valuable insights for shaping differentiated RW policies and offers a theoretical foundation for sustainable water resource planning, with important implications for achieving SDG6 and improving national water security.