In the framework of heterogeneous biocatalysis in non-aqueous media, knowledge of water adsorption curves is necessary for the choice of operating conditions. Indeed, water content plays a crucial role in the performance of such enzymatic reactors. A method to estimate water adsorption curves in biphasic solid-fluid systems is proposed here. It is grounded on the hypothesis that the water adsorption of the solid is not dependent on the solvent and on the theoretical evaluation of water activity in the solvent. It is tested in the case of 3-methyl-1-butanol, 5-methyl-2-hexanone and supercritical carbon dioxide as solvents and an immobilized enzyme, Lipozyme(R), as the solid phase. The method proved to be in good agreement with experiments. The method uses only a single experimental curve but necessitates the development of numerical modeling of thermodynamics. However, a simplified method, restricted to the range-hydrophobic to weakly hydrophilic solvent-is also proposed and tested.