Heat pump comprising: an evaporator for evaporating water as a working liquid to generate a working vapor, the evaporator comprising an evaporation chamber and being configured to generate an evaporation pressure of less than 20 hPa within the evaporation chamber, so that the water will evaporate at temperatures below 18°C; a compressor-liquefier system comprising: a compressor coupled to the evaporator for compressing the working vapor, the compressor being configured as a continuous-flow machine and further being configured to compress the working vapor to a working pressure of more than 5 hPa above the evaporation pressure; and a liquefier for liquefying a compressed working vapor, the liquefier being configured to output a heat which has been obtained during the liquefaction to a heating system, wherein the compressor comprises several flow machines (172, 174) arranged one behind the other so as to compress the working vapor to an intermediate pressure by a first flow machine and to compress the working vapor to the working pressure by a last flow machine, and wherein one or more heat exchangers are arranged downstream from a first flow machine or a further flow machine, the one or more heat exchangers being configured to cool the working vapor heated by a previous flow machine, characterized in that the one or more heat exchangers is/are configured to extract heat from the heated working vapor by cooling the working vapor heated by the previous flow machine, so as to heat water with the extracted heat, and the several flow machines (172, 174) arranged one behind the other are mutually independent flow machines which are controllable independently of one another with regard to their rotational speeds, so that two flow machines (172, 174) of the several flow machines (172, 174) arranged one behind the other may have different rotational speeds. an evaporator for evaporating water as a working liquid to generate a working vapor, the evaporator comprising an evaporation chamber and being configured to generate an evaporation pressure of less than 20 hPa within the evaporation chamber, so that the water will evaporate at temperatures below 18°C; a compressor-liquefier system comprising: a compressor coupled to the evaporator for compressing the working vapor, the compressor being configured as a continuous-flow machine and further being configured to compress the working vapor to a working pressure of more than 5 hPa above the evaporation pressure; and a liquefier for liquefying a compressed working vapor, the liquefier being configured to output a heat which has been obtained during the liquefaction to a heating system, wherein the compressor comprises several flow machines (172, 174) arranged one behind the other so as to compress the working vapor to an intermediate pressure by a first flow machine and to compress the working vapor to the working pressure by a last flow machine, and wherein one or more heat exchangers are arranged downstream from a first flow machine or a further flow machine, the one or more heat exchangers being configured to cool the working vapor heated by a previous flow machine, characterized in that the one or more heat exchangers is/are configured to extract heat from the heated working vapor by cooling the working vapor heated by the previous flow machine, so as to heat water with the extracted heat, and the several flow machines (172, 174) arranged one behind the other are mutually independent flow machines which are controllable independently of one another with regard to their rotational speeds, so that two flow machines (172, 174) of the several flow machines (172, 174) arranged one behind the other may have different rotational speeds. a compressor coupled to the evaporator for compressing the working vapor, the compressor being configured as a continuous-flow machine and further being configured to compress the working vapor to a working pressure of more than 5 hPa above the evaporation pressure; and a liquefier for liquefying a compressed working vapor, the liquefier being configured to output a heat which has been obtained during the liquefaction to a heating system, wherein the compressor comprises several flow machines (172, 174) arranged one behind the other so as to compress the working vapor to an intermediate pressure by a first flow machine and to compress the working vapor to the working pressure by a last flow machine, and wherein one or more heat exchangers are arranged downstream from a first flow machine or a further flow machine, the one or more heat exchangers being configured to cool the working vapor heated by a previous flow machine, characterized in that the one or more heat exchangers is/are configured to extract heat from the heated working vapor by cooling the working vapor heated by the previous flow machine, so as to heat water with the extracted heat, and the several flow machines (172, 174) arranged one behind the other are mutually independent flow machines which are controllable independently of one another with regard to their rotational speeds, so that two flow machines (172, 174) of the several flow machines (172, 174) arranged one behind the other may have different rotational speeds.