Water scarcity and energy crisis have recently become two severe global problems. Low-grade waste heat, a substantial byproduct of energy consumption, promises to provide safe water by driving sorption-based atmospheric water harvesting (SAWH) device. Herein, a low-grade waste heat-driven atmospheric water generator (LWG) is constructed with rapid kinetics at the system level. Solely in 3 h, the device obtains 1.766 g g−1 of water productivity and up to 98 % of water recovery ratio driven by 120 °C of waste heat. Further, an optimized multi-cycle operation strategy is proposed to guide LWG's daily water harvesting, enabling it to predictably obtain over 15 kg m−2 day−1 water productivity by maximizing systemic sorption and desorption-condensation rates. The strategy not only is widely suitable for all SAWH devices, but also provides a universal optimization guideline for sorption-based dehumidification, thermal storage, and electric thermal management.