Precision Accounting and Targeted Allocation of High-Quality Water in Protected Areas: A Source–Flow–Use Framework Applied to Hainan Tropical Rainforest National Park

High-quality water resources (HQWRs) generated in ecological conservation areas, such as national parks, constitute critical ecosystem products. However, conventional water allocation frameworks often overlook ecological provenance and fail to ensure compensation for source regions. This study developed a spatially explicit “source–flow–use” accounting framework to quantify HQWR supply, allocation patterns, and ecological contributions at the watershed scale. By integrating land-use, hydrological, and sectoral water-use data, the framework identifies HQWRs originating from protected areas and tracks their distribution across economic sectors. Using Hainan Tropical Rainforest National Park as a case study, land-use, hydrological, and water-use data were integrated to calculate contribution ratios. They revealed that over one-third of HQWRs is consumed by agriculture, while the industrial and domestic sectors—despite their higher water quality demands—receive disproportionately small shares. Approximately 52 billion m 3 of HQWRs remains underutilized in terms of ecological and economic values, highlighting mismatches in distribution. The framework provides a replicable metric for ecological compensation, differentiated pricing, and governance, crediting pristine water at its source rather than downstream transformations. By linking HQWR accounting to policy and management, this framework supports targeted allocation, promotes sustainable water use, and offers a practical basis for integrating protected-area ecosystem services into regional water governance.