In this work, we present a practical approach combining experimental and theoretical analyses to assess water evaporation in Arabica coffee leaves. We examine continuously the changing water content of leaves through optical reflectance spectroscopy and mass loss measurements, beginning from a fully saturated stage and extending beyond the turgor loss point. We establish a relationship between the current water content and the dielectric function, based on the changing of the molecular water dipoles inside the leaf due to evaporation.