Energy reducer for house building drainage system

The invention provides an energy reducer for a house building drainage system, and solves the problem that the internal structure of an existing energy reducer is worn quickly due to the fact that the internal structure of the existing energy reducer directly blocks the water flow direction with large kinetic energy from a high road to a lower road to change the flowing direction of the water flow. The water-saving device comprises a vertically-arranged main pipe, the main pipe is of a vertically-through tubular structure, the upper end of the main pipe is detachably and hermetically connected with the lower end of an upper water-saving pipe, the lower end of the main pipe is detachably and hermetically connected with the upper end of a lower water-saving pipe, and the interiors of the upper water-saving pipe, the main pipe and the lower water-saving pipe are vertically communicated; a kinetic energy counteracting device is fixedly arranged in the main pipe and comprises a vertically-through straight pipe whi