Abstract: Disclosed are a self-closing water saving device, method, and toilet. The self-closing water saving device for mounting in a tank of a toilet bowl is used for supplying water to the tank, and is characterized by comprising: a water inlet adapted to be connected to an external water source, a water outlet adapted to provide water to the tank, and a jet-propelling port for jetting water to the bottom of a water trap of the toilet bowl or the bottom of a sewer; wherein, when the tank discharges water to the water trap, the water jetted from the jet-propelling port is used to propel the water which is discharged from the tank and flows into the water trap, the bottom of the water trap, or the bottom of the sewer.