In this work the relationship between structure and water sorption for epoxy films was studied using electrochemical impedance spectroscopy. It is shown that the electrochemical impedance spectroscopy can be applied to obtain information about the amount of water absorbed by the epoxy film and the water permeation through the film, while only the amount of water absorbed is obtained from the ''sorption method''. The free volume is the decisive factor for both the amount of water in the cured epoxy film and water permeation through the film.