<p>Water-based triboelectric nanogenerators (TENGs) have recently attracted attention as promising solutions for distributed micro energy harvesting. These devices provide a way to provide sustainable power to low-power electronics and self-driving sensors by converting the kinetic energy of water droplets, flowing water, and sea waves into electricity through contact electrification and electrostatic induction. This review provides a comprehensive overview of recent progress focused on the working mechanisms, structural design, and performance improvements in various water environments of water-based TENGs. Key mechanisms such as bulk-effect water droplet-based electricity generation and electrode ground capacitance are summarized. Finally, we discuss current challenges and prospects for scalable and durable self-driving systems, along with their potential applications in environmental monitoring, wearable electronics, and marine sensing.</p>