Keep the manufacturer's required flow during operation and the prescribed finishing rinse. Reducing water below that requirement is not a sound way to assess whether the appliance is economical.
What the observation tells you
For a practical estimate, consider the normal tap flow and the total time it runs during real sessions, including rinsing. A manufacturer's average for another model or household is not an exact measure of yours. Avoid prolonged empty running solely to create a measurement.
A useful next step
If water use concerns you, reduce the amount of waste needing processing and use an appropriate separate collection route. Never compromise the operating instructions to achieve a lower figure.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.