County-level water networks, as the “last mile” of China’s national water network system, play an important role in improving the spatial balance of regional water resources through optimized allocation. Existing studies mostly focus on high-level water networks, paying insufficient attention to county-level networks with a small engineering scale and low storage capacity. Therefore, this study constructs a multi-source and multi-user optimal allocation model with the goal of minimizing the water supply-demand mismatch. This study takes the county-level water network of Renhe District, Panzhihua, as an example, and conducts the optimal allocation and spatial balance evaluation of water resources according to the three stages of “decentralized management, unified management of irrigation areas, and networked collaborative allocation”. The results indicate that: the water network allocation significantly improves water resource allocation efficiency and reduces regional water scarcity through mutual support among water sources; the water transfer structure exhibits a collaborative pattern of “expanding from midstream to upstream, prioritizing nearby water sources, and supplementing with distant water sources”, significantly enhancing system resilience; the water network allocation promotes spatial balance, particularly under the extreme supply-demand condition; and due to the structural constraints of county-level water networks, optimization on the supply side alone cannot fundamentally resolve the water scarcity problem, and a sustainable development path combining supply and demand management should be established.