Adsorption isotherms of pure water in zeosils were computed with GCMC simulations using the RASPA simulation package. We screened several values of the chemical potential of the fictitious water reservoir to compute the number of adsorbed water molecules by using the relationship between chemical potential of water and hydrostatic pressure µ water (P ). In order to explore phase space, translation, rotation and swap moves were applied to water molecules, in a ratio of 1:1:2 respectively. Each simulation consists of 2× 10 5 equilibration cycles followed by 10 5 production cycles, during which average quantities were calculated.