High-rise building auxiliary water supply system capable of utilizing building drainage energy

A high-rise building auxiliary water supply system capable of utilizing building drainage energy comprises a low-region water tank, a middle-region water tank and a high-region water tank. The special points are that the high-rise building auxiliary water supply system also comprises a high-region drainage vertical pipe, a middle-low-region drainage vertical pipe and a pressure water supply tank, wherein the pressure water supply tank is divided into an inner cavity and an outer cavity by a diaphragm; a sanitary wastewater buffering box is arranged between the high-region drainage vertical pipe and the middle-low-region drainage vertical pipe; the sanitary wastewater buffering box is higher than the middle-region water tank; a drainage pipe is arranged at the bottom of the sanitary wastewater buffering box; the drainage pipe is communicated with the inner cavity of the pressure water supply tank through an electromagnetic three-way valve; the low-region water tank is communicated with an inlet of the outer ca