<p>Dongting Lake (DTL) is situated on the south bank of the Jingjiang section in the middle reaches of the Yangtze River. The rapid urbanization and demographic shifts in the DTL region have altered regional water demand and revealed disparities in the availability of high-quality water resources (HQWRs). This study employed water quality assessment methods to classify the quality grades of water resources using long-term monitoring data from the DTL area. By incorporating actual urban and rural water demand, a predictive evaluation was conducted on the water resource supply–demand balance for future planning years (2035, 2050). Furthermore, based on the spatial distribution of water resources in the DTL and the projected water supply–demand data for planning years, this study employed the NSGA-II optimization algorithm to conduct a multi-objective optimization of water resource allocation. The results indicate that although the total designed water supply capacity (17.98 × 10⁸&#xa0;m³) exceeds actual usage (11.79 × 10⁸&#xa0;m³), only 40.2% of domestic water comes from HQWRs. Despite total surface water remaining sufficient under future scenarios, overall scarcity rates escalate to 13.7% in 2035 and 17.0% in 2050, and shortages of HQWRs are projected to rise from 42.5 to 49.4%. The multi-objective optimization of water supply solutions (Schemes 1–4) has significantly improved the reliability (Re) of water supply in DTL area, with the overall Re rising from 0.588 to 0.936. Notably, Yiyang, which relies on groundwater, exhibited the greatest improvement in Re. The results underscore the spatial disparity between water quality and water supply capacity, emphasizing the pressing need for targeted optimization in infrastructure construction and water quality assurance. This initiative seeks to foster the sustainable development and equitable distribution of resources in the DTL area, offering a reference for future urban and rural water resource allocation in the area.</p>