High-quality water resources conserved by national parks and other protected areas are indispensable ecological products for maintaining watershed ecological security and supporting downstream socio-economic systems. However, existing water management frameworks have not effectively identified or calculated their ecological spillover values, resulting in "high-quality but low-efficiency" allocation, reduced distributional equity, and insufficient protection incentives. This study introduces the Paracommons theory, which conceptualizes high-quality water not as an ordinary public good, but as a scarce ecological asset "released" through conservation activities, thereby requiring dedicated accounting, allocation, and compensation mechanisms. Taking the National Park of Hainan Tropical Rainforest as a case study, a three-tier "source-flow-use" accounting framework was established. The results show that, in terms of overall water allocation within the park, high-quality water constitutes an important share of regional water use, yet much of it is directed toward sectors with relatively low water quality requirements, while high-value industries and domestic users that rely more critically on high-quality water receive limited supply. This reflects a mismatch between water quality and economic value realization. At the watershed scale, different river basins exhibit heterogeneous patterns—such as agriculture-dominated, industry-dependent, or domestic-oriented allocations—highlighting the structural imbalance in high-quality water distribution. Drawing on domestic practices and international experiences, the study proposes a closed-loop market-oriented mechanism of "clarification of rights, pricing, trading, and financialization" for high-quality water, including graded entitlement based on source, quality, and ecological contribution. We further recommend innovative financial instruments such as water-ecological service credits, and a "high-quality water bank", and strengthened institutional and regulatory safeguards. This framework aims to advance the realization of ecological product values in protected areas and offer universally applicable insights for global natural resource governance.