To construct a system for removing refuse adhering to a screen of a water tank without spending much cost.

There is provided a method of operating the refuse removing system 1 which is applicable to the case where water from a water source is introduced via the water tank 10 to a water turbine 17 of a generator 18 in a hydro-electric power generating facility. The refuse removing system functions to remove refuse 20 adhering to the screen 15 for catching the refuse 20 contained in the water from the water source by jetting gas or water toward the screen 15 by a jetting means 2 arranged on a bottom 10a of the water tank 10. According to the method, a water level of the water tank 10 is detected, and an output of the generator 18 is detected, followed by activating the jetting means 2, based on the detected water level and the detected output.