A method for heating white liquor or a mixture of white liquor and another liquid for use in a digester system of a chemical pulp mill, the method including the steps of: producing black liquor in the digester system; extracting black liquor from the digester system, flashing the extracted black liquor and thereby generating flashed black liquor and flash vapor; directing the flash vapor through a heat exchanger to heat a white liquor flowing through the heat exchanger; the flashed black liquor flows to at least one of a heat recovery or evaporation stage, and the heated white liquor flows to the digester system.