Harvesting environmental energy is an effective and sustainable route for realizing self‐powered electronics. Here, a fully‐enclosed metal electrode‐free self‐adaptive triboelectric nanogenerator (TENG) based on liquid–solid triboelectrification by using a PTFE cylinder partly full of water is reported by authors. The water‐based TENG delivers an open‐circuit voltage of 15 V and short‐circuit current of 0.3 μA, respectively, when being waggled airily. The output performances of the TENG under different liquid portions, water volumes, and shaking frequencies are investigated by coupling of simulations. With advantages of simplicity and adaptability, the TENG is worn on the human body readily. Under a casual walking and running, a water‐based TENG made of a mineral water bottle gets both output voltages of more than 5 V. Further, it is proved that our TENG serves as a sustainable power source to drive personal electronics by integrating with a capacitor. Given its desirable output performance and excellent adaptability, the water‐PTFE metal electrode‐free TENG provides a promising and feasible approach for harvesting diverse vibrational energies in a harsh environment and serve as an alternative power source for driving small electronics.