Provided is a water purifier that includes a filtering unit for producing purified water by filtering influent water; a TDS measuring unit for measuring the total dissolved solids (TDS) in the water flowing into the filtering unit; a purified water passage through which the purified water is discharged; a concentrated water passage through which concentrated water, filtered by the filtering unit, is discharged; a concentrated water flow control valve for controlling the flow rate of the concentrated water discharged through the concentrated water passage; and a control unit for adjusting the degree of opening and closing of the concentrated water control valve, on the basis of the TDS and the pressure of the water flowing into the filtering unit.