A self-sustaining sensor platform is a core component for Internet-of-Things and smart-grid systems. However, monitoring, processing, and displaying the minute changes of a targeted-environmental element in a real-time fashion without external power sources is challenging because of a practical difficulty of doing energy harvesting and analysis of dynamics at the same time. Here, we present a self-sustaining water-motion-sensing (SS-WMS) platform to monitor and display the time-varying dynamics of water-motion, i.e., frequency and amplitude, using only the energy harvested from the water-motion itself. A water-contact triboelectric nanogenerator (WC-TENG) produces electrical energy, correlated with the repetitive squeezing and releasing of a water droplet. The SS-WMS integrated circuit (IC) harvests the energy and simultaneously analyzes the dynamics of water-motion, which is converted into binary codes to be displayed through LEDs powered by the gathered energy. The proposed platform would contribute to advanced sensing functions of a self-sustaining system for various targeted-ambient elements.