Asymmetry Between Water Management Efficiency and Balanced Development in the EU and the Three Seas Initiative Countries—Comparative Analysis

Dynamic economic growth and climate change increase pressure on water resources, posing a challenge to achieving sustainable development goals, especially in regions with diverse hydrological conditions and development trajectories. This study aims to quantitatively assess the dynamic asymmetry between water management efficiency and the level of sustainable development in the European Union and the Three Seas Initiative (3SI) countries, with particular emphasis on cumulative mechanisms, regional divergence, and the potential low equilibrium trap. The values of the analysed indicators were calculated for 2015, 2021, and 2022, and subsequently their changes were determined for 2021/2015 and 2022/2021. This study was conducted using Eurostat data, applying the CRITIC method for objective weight determination, the TOPSIS technique for constructing synthetic measures, the Kruskal–Wallis and Mann–Whitney tests to assess inter-group differences, and linear regression to identify dependencies. Countries were grouped according to the dynamics of changes in the synthetic water management index. The results indicate a clear asymmetry: the water sector is characterised by a cumulative mechanism and strong divergence (particularly evident in the short period), whereas sustainable development remains significantly more stable, homogeneous, and weakly linearly correlated with previous water achievements. In 3SI countries, a higher rate of improvement in water indicators was observed compared to the rest of the EU; however, no significant synergy with progress in sustainable development was found. The negative impact of the Water Exploitation Index on sustainable development is statistically noticeable but does not confirm the existence of a clear “low equilibrium trap” across the entire 3SI region. This study highlights the need for regionally differentiated, asymmetrical water policies and the integration of water management with broader ecological transformation strategies.