"Water behavior in pure silicalite and Dealuminated Zeolite Y (DAY), two highly hydrophobic zeolites, was investigated at different temperatures in the range 100-600 K by molecular dynamics simulations. The Compass forcefield was used to carry out the study. A full flexibility of water molecules and of the zeolite framework was considered. The results show that water behavior is more complex in silicalite than in zeolite DAY. Three different activation energies for water diffusion were obtained in silicalite in the range 250-600 K compared to two for DAY. The values of these activation energies are discussed in detail and are related to the hydrogen bond‘s strength and the zeolite structure. Moreover, from the radial distribution functions (rdfs), it is shown that water mostly exists in the gas phase at room temperature in silicalite whereas liquid water is observed in DAY in agreement with previous experimental observations. The self-diffusion coefficients of water and the rdfs are obtained as a function of temperature in order to explain the behavior differences of water in the two all-silica zeolites. The loading influence on the self-diffusion coefficients is also investigated for both crystals. The results are compared with previous experimental and theoretical studies."