Method for energy-saving continuous measuring of the quality of a fluid, in particular water, with a sensor (1, 1a) for capturing a measured quantity, wherein: S1) the sensor (1, 1a) is provided as part of a measuring device for measuring the liquid quality and the measuring device is arranged relative to the fluid; S2) the sensor (1, 1a) is alternately activated for the duration of a switch-on phase and deactivated for the duration of a switch-off phase; S3) a switch-on phase in a steady state of the sensor (1, 1a) is defined as a defined switch-on phase and a measured value is determined with the sensor (1, 1a) during the defined switch-on phase as a comparative measured value is captured, the steady state being reached when a value of the measured quantity differs by at most a predetermined difference from a value of the measured quantity during a previous switch-on phase; S4) a reference measurement is performed to capture a measured value representing the liquid quality as a reference measured value; S5) with the sensor (1, 1a) during further switch-on phases, which follow the defined switch-on phase, measured values are continuously captured as operating measured values; S6) a calculation method is defined which assigns the comparative measured value to the reference measured value; and S7) a final measured value for measuring the quality is determined from each operating measured value by means of the calculation method; characterized in that for carrying out the reference measurement S4b) the defined switch-on phase or a switch-on phase between the defined switch-on phase and the further switch-on phases is extended compared to the previous switch-on phases in order to capture the operating measured values, and during the extended switch-on phase the reference measured value is captured with the sensor (1, 1a). S1) the sensor (1, 1a) is provided as part of a measuring device for measuring the liquid quality and the measuring device is arranged relative to the fluid; S2) the sensor (1, 1a) is alternately activated for the duration of a switch-on phase and deactivated for the duration of a switch-off phase; S3) a switch-on phase in a steady state of the sensor (1, 1a) is defined as a defined switch-on phase and a measured value is determined with the sensor (1, 1a) during the defined switch-on phase as a comparative measured value is captured, the steady state being reached when a value of the measured quantity differs by at most a predetermined difference from a value of the measured quantity during a previous switch-on phase; S4) a reference measurement is performed to capture a measured value representing the liquid quality as a reference measured value; S5) with the sensor (1, 1a) during further switch-on phases, which follow the defined switch-on phase, measured values are continuously captured as operating measured values; S6) a calculation method is defined which assigns the comparative measured value to the reference measured value; and S7) a final measured value for measuring the quality is determined from each operating measured value by means of the calculation method; characterized in that for carrying out the reference measurement S4b) the defined switch-on phase or a switch-on phase between the defined switch-on phase and the further switch-on phases is extended compared to the previous switch-on phases in order to capture the operating measured values, and during the extended switch-on phase the reference measured value is captured with the sensor (1, 1a).