A method for evaporation and possibly distillation of liquids by means of a heat pump is provided. By using a heat pump (2), energy is taken from energy reservoir(s) (1) such as rivers, sea water, air, or ground heat. However, it is difficult to obtain temperatures high enough to evaporate water at atmospheric conditions. According to the invention, low temperature heat is utilized by means of a heat pump by using the condenser of the heat pump to evaporate liquids in an evaporator (4′) at a pressure lower than atmospheric pressure, and thus at a lower evaporation temperature. Furthermore, the saturation of the evaporated liquids is eliminated before the evaporated liquids enter the compressor (10) by the further heating of the evaporated liquids leaving the liquids evaporator (4′) in a heat exchanger (11) that utilizes the peak temperature of the refrigerant that leaves the heat pump's refrigerant compressor (3).