In recent years, the advent of the smart era has confronted a novel “energy crisis”—the challenge of distributed energy provision, necessitating an imperative for clean energy development. Encompassing 71% of the Earth’s surface, water stands as the predominant conduit for energy transfer on our planet, effectively harnessing a fraction thereof to fulfill global energy demands. Modern hydropower technology primarily harnesses concentrated low-entropy water energy. However, the majority of natural water energy is widely dispersed in the environment as high-entropy distributed water energy, encompassing raindrop energy, stream energy, wave energy, evaporation energy, and other small-scale forms of water energy. While these energies are readily available, their collection poses significant challenges. Consequently, researchers initiated investigations into high-entropy water energy harvesting technology based on the electrodynamic effect, triboelectric effect, water volt effect, and other related phenomena. The present paper provides a comprehensive review of high-entropy water energy harvesting technologies, encompassing their underlying mechanisms, optimization strategies, and diverse applications. The current bottlenecks of these technologies are comprehensively analyzed, and their future development direction is prospectively discussed, thereby providing valuable guidance for future research on high-entropy water energy collection technology.