Toilet water saving apparatus linkable with bidet, and water saving method thereof

Disclosed herein is a toilet water saving apparatus linkable with a bidet, and a water saving method thereof. The water saving apparatus comprises branch tubes connected to the supply tube for supplying the washing water to the water reservoir and the bidet, respectively, a three-way valve installed to the branch tubes therebetween, and a urination water level sensor and a defecation water level sensor installed inside the water reservoir of the toilet for detecting a urination water level and a defecation water level. The three-way valve has a reservoir valve and a bidet valve for allowing the washing water to be selectively supplied to one or both of the bidet and the water reservoir. The bidet valve of the three-way valve is adapted to be opened or closed by a controller as a bidet button provided at the control pad is operated, and the reservoir valve of the three-way valve is adapted to be opened or closed by the controller according to the operation of a washing button or a supplement button provided at the control pad and according to signals from the urination water level sensor and the defecation water level sensor. The present invention results in prevention of unnecessary and significant consumption of water which is not required to flush urine.