<p>Strategic planning of national-scale water networks requires evaluating both connectivity and the physical difficulty of water intake and conveyance. We propose a reproducible framework to quantify comprehensive accessibility (CA) for the pan-basin water network connecting the Yangtze, Yellow, Huai, and Hai basins by integrating topology-derived accessibility with resistance-based intake constraints. Results show that engineered links shift the natural mainstream-led structure toward a more interconnected, multi-core configuration, while western headwaters remain persistently constrained by steep terrain and high resistance. CA exhibits a clear core–periphery pattern: high values cluster in low-relief plains and dense lake–river systems, whereas localized depressions occur at urban crossings where resistance increases despite dense canal–river meshes. Sub-basin results indicate scale dependence, with configuration advantage dominating basin-level ordering and resistance acting through corridor-scale hotspots. CA, as a comparative screening indicator, is intended to provide an interpretable basis for early-stage corridor screening and staged investment.</p>