This study explores the spatial coupling of water purification ecosystem service (WPS) supply, demand, and flow in the Yangtze River Delta Eco-Green Integration and Development Demonstration Zone. Using quantitative models and the SPANS algorithm, we analyze WPS supply-demand balances and flows at multiple scales. Results reveal significant spatial heterogeneity, with supply surpluses near lakes and deficits in urban areas. Flow simulations show WPS converging in central and northern regions. Based on these findings, we propose an ecological compensation design tailored to regional supply-demand characteristics. Our study highlights the need for refined compensation policies, considering spatial heterogeneity and dynamic flow patterns. The research provides insights into optimizing water ecological resources and promoting sustainable regional development in the Yangtze River Delta. This comprehensive study delves into the intricate interplay between supply, demand, and flow dynamics of freshwater ecosystem services (FES), particularly WPS, within the Yangtze River Delta Ecological Green Integration Development Demonstration Zone (henceforth referred to as the 'Demonstration Zone’). The Demonstration Zone, situated in the economically vibrant Yangtze River Delta region, faces mounting pressures on its aquatic ecosystems due to rapid urbanization, industrialization, and climate change. Consequently, understanding and managing the provision of vital FES, such as water purification, has become paramount for ensuring sustainable development and ecological resilience. The study commences with a rigorous quantification of the supply and demand for nitrogen and phosphorus water purification services across the Demonstration Zone. Employing the InVEST model, we analyzed high-resolution spatial data to map the distribution of these services at sub-basin and grid cell levels. The results highlight substantial spatial heterogeneities in the supply-demand balances, with significant deficits identified in key areas such as the southeast of Taihu Lake and the periphery of the Demonstration Zone. These findings underscore the urgent need for targeted interventions to address the mismatch between the availability of WPS and the escalating demands driven by population growth and economic activities. To gain deeper insights into the flow of WPS, we applied the Service Path Attribution Networks (SPANS) algorithm. This innovative approach enabled us to simulate the dynamic movement of ecosystem services across the landscape, revealing the complex interplay between supply surplus and deficit regions. Our analysis revealed distinct flow patterns, with water purification services primarily flowing from forested and wetland areas, where suppl慹渠摩⁳猠瑡慢歵敮桤潡汮摴攬爠獴睷潡牲此楳渠杵⁲瑢潡睮愠牡摮獤†獡畧獲瑩慣極湬慴扵汲敡搠敺癯敮汥潳瀠海敩湴瑨†慨湩摧⁨敥捲漠汤潥杭楡据慤氮†捎潯湴獡敢牬癹愬琠楴潨湥†楣湥瑴桲敡夠慡湮杤琠穮敯⁲剴楨癥敲牮†䑰敡汲瑴慳†慯湦搠⁴扨敥礠潄湥摭⹯nstration Zone emerged as key convergence zones for these ecosystem service flows, highlighting their crucial role in maintaining regional water quality. Building upon these insights, we propose a multi-faceted ecological compensation design tailored to the unique ecological and socio-economic context of the Demonstration Zone. The proposed design aims to incentivize conservation efforts and promote equitable distribution of ecological benefits. Specifically, it emphasizes the need for differential compensation strategies based on the supply-demand dynamics identified in our analysis. For instance, regions providing essential WPS should be rewarded with financial incentives and policy support to sustain their ecological contributions. Conversely, regions with high demand but limited supply capacity should be encouraged to adopt pollution reduction measures and invest in alternative water treatment technologies. Moreover, our proposed compensation suggestions incorporate adaptive management principles, recognizing the dynamic nature of ecosystem services. We advocate for the establishment of a monitoring and evaluation framework that continuously tracks changes in supply-demand balances and service flows. This information will inform periodic adjustments to compensation standards and strategies, ensuring their relevance and effectiveness over time. In conclusion, this study represents a significant contribution to the understanding and management of freshwater ecosystem services, particularly WPS, in rapidly developing regions. By integrating quantitative modeling, spatial analysis, and policy recommendations, we have illuminated the complex sup-ply-demand dynamics within the Demonstration Zone and proposed practical solutions to address the challenges posed by ecological mismatches. Our findings not only advance scientific knowledge but also offer actionable insights for policymakers, practitioners,