Method for energy-saving continuous measuring (FM) of the quality of a fluid, in particular water, with a sensor for capturing a measured quantity (G), wherein: S1) the sensor 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 is alternately activated for the duration of a switch-on phase (TE) and deactivated for the duration of a switch-off phase (TA); S3) a switch-on phase (TE) in a steady state of the sensor is defined as a defined switch-on phase (TED) and a measured value (M) is determined with the sensor during the defined switch-on phase (TED) as a comparative measured value(V) is captured, the steady state being reached when a value (W) of the measured quantity (G) differs by at most a predetermined difference (D) from a value (W) of the measured quantity (G) during a previous switch-on phase (TE); S4) a reference measurement (RM) is performed to capture a measured value (M) representing the liquid quality as a reference measured value (R); S5) with the sensor during further switch-on phases (TEW), which follow the defined switch-on phase (TED), measured values (M) are continuously captured as operating measured values (B); S6) a calculation method is defined which assigns the comparative measured value (V) to the reference measured value (R); and S7) a final measured value (F) for measuring the quality is determined from each operating measured value (B) by means of the calculation method; characterized in that for carrying out the reference measurement (RM) S4b) the defined switch-on phase (TED) or a switch-on phase (TEV) between the defined switch-on phase (TED) and the further switch-on phases (TEW) is extended compared to the previous switch-on phases (TE) in order to capture the operating measured values (B), and during the extended switch-on phase (TEV) the reference measured value (R) is captured with the sensor . S1) the sensor 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 is alternately activated for the duration of a switch-on phase (TE) and deactivated for the duration of a switch-off phase (TA); S3) a switch-on phase (TE) in a steady state of the sensor is defined as a defined switch-on phase (TED) and a measured value (M) is determined with the sensor during the defined switch-on phase (TED) as a comparative measured value(V) is captured, the steady state being reached when a value (W) of the measured quantity (G) differs by at most a predetermined difference (D) from a value (W) of the measured quantity (G) during a previous switch-on phase (TE); S4) a reference measurement (RM) is performed to capture a measured value (M) representing the liquid quality as a reference measured value (R); S5) with the sensor during further switch-on phases (TEW), which follow the defined switch-on phase (TED), measured values (M) are continuously captured as operating measured values (B); S6) a calculation method is defined which assigns the comparative measured value (V) to the reference measured value (R); and S7) a final measured value (F) for measuring the quality is determined from each operating measured value (B) by means of the calculation method; characterized in that for carrying out the reference measurement (RM) S4b) the defined switch-on phase (TED) or a switch-on phase (TEV) between the defined switch-on phase (TED) and the further switch-on phases (TEW) is extended compared to the previous switch-on phases (TE) in order to capture the operating measured values (B), and during the extended switch-on phase (TEV) the reference measured value (R) is captured with the sensor . <EOS>