The paper is based on the fact of serious water shortage and the coming of a LC ( low carbon ) lifestyle. The design was guided by demand design and aided by Fluent simulation, it break the normal method of water sav- ing and works out a set of a no power consumption new system of house water saving. The paper makes a detailed presentation of the design ideas and process of a system core ; the simulation result can show the three-dimensional flow and pressure distribution of flow in a system core factuaUy. Consequently, the simulation demonstrates the feasibility and practical applicability of the design.