A method and an apparatus for regulating the amount of liquid in the wet cleaning of a gas in at least two stages are disclosed. In the method, liquid from at least one of the stages after the first stage is brought into contact with air, such that the liquid is partly evaporated and cooled, the evaporation being carried out in such a manner that the amount of liquid in the stage remains the same, whereupon the remaining liquid is heated before being recycled to the wet cleaning. The apparatus comprises a scrubber (6) having at least two stages and a liquid-circulation circuit (53) in at least one of the stages after the first stage, the liquid-circulation circuit (53) including an evaporator (20) adapted to evaporate liquid to such an extent that the amount of liquid in the stage remains the same and to cool liquid from the circuit by contacting it with air, as well as a heater (44) adapted to heat the cooled liquid in the circuit.