Analysis of the water role in STM image formation processes for organic thin films was performed in this work. The contribution of the water shell covering the film was considered under the assumption that no water can be inside the film molecules. Conducting thin films were chosen as objects and they were measured under different humidity conditions. The images were processed for calculating their average corrugation. The relationship of the corrugation with the relative humidity was outlined and compared with a theoretical model of water adsorption. Finally, nanogravimetric and contact angle measurements were performed as independent proofs of the water adsorption model.