Water purifier

A water purifier, comprising:

• a filter unit having a reverse osmosis membrane filter in order to generate purified water;
• a supply valve opened and closed so that water is supplied to the reverse osmosis membrane filter;
• an instantaneous heating device having a water inlet supplied with purified water, having been filtered by the filter unit, and a water outlet having the purified water heated and discharged therefrom, and heating the purified water flowing into the water inlet and flowing out to the water outlet, so that hot water is discharged through the water outlet;
• an extraction member provided for extracting the hot water discharged from the instantaneous heating device;
• a supply pump operating in order to supply purified water to the water inlet of the instantaneous heating device;
• a domestic water drainage line from which domestic water, having not been filtered by the reverse osmosis membrane filter is discharged;
• a hot water drainage line from which drain water, having been drained from the instantaneous heating device is drained;
• a hot water drainage valve provided in the hot water drainage line so as to open and close the hot water drainage line;
• and
• a control unit controlling the valves and opening and closing of respective flow passages of the hot water drainage line and the domestic water drainage line so that, among a hot water drainage process through the hot water drainage line, and a domestic water drainage process through the domestic water drainage line, the hot water drainage process is carried out first.