This invention concerns a method to detect the wetness state of a vehicle windshield surface (S) comprising a windshield wiper unit (1), the windshield wiper unit (1) comprising: —wiper blades (5) configured to wipe the windshield surface (S) when set in motion, —at least one motor (7) configured to set the wiper blades (5) in motion, —a controller (9), configured to control the at least one motor (7), the method comprising the steps: —measuring the power consumption of the at least one motor (7), —determining the wiping speed (W) of the wiper blades (5), —using the measured power consumption and determined wiping speed (W) to deduce a friction related coefficient of the windshield surface (S), —comparing the deduced value to at least one predetermined value in order to determine the wetness state of the vehicle windshield surface (S).