We first investigated the effect of local defects on pure water intrusion inside silicalite-1 and chabazite. In Figure , we plot the intrusion isotherm of TIP4P water using GCMC simulations for defect-free model of silicalite-1 and chabazite, and compare it to the isotherms with either weak or strong silanol defects. The "weak" silanol defect model provides a representation of defects observed in zeolites synthesized in hydroxide (HO -) media. In order to keep a zeolite model as simple as possible, the "strong" defect model attempts to mimic more hydrophilic defects, such as Si-O -,Na + without modifying the defect geometry, but only its charge distribution. Let us first discuss the intrusion of water in presence of weak defects. In all cases, the isotherms are of type V according to the IUPAC classification, 62 and condensation takes place above bulk water vapor pressure (P 0 ∼ 5300 Pa for the TIP4P model ), as in the case of the defect-free models. This indicates that the framework system remains hydrophobic, regardless of the defect content. By increasing the number of defects, the forced intrusion (capillary evaporation) is shifted towards lower pressure. The similarity of qualitative hydration behavior regardless of defect content (i.e., the same shape of the isotherms) is worth being examined in more detail by examining the thermodynamics of water intrusion. In Fig- In presence of weak defects (top and bottom left panels on Figure ), the evolution of potential energy is consistent with the hydrophobic nature of the framework because at low water content, the potential energy per water molecule is below the bulk cohesion energy of water -indicating that water would rather stay in the bulk rather than penetrate the framework. The presence of defects helps lowering the water-water energy to -27 kJ.mol -1 .molec. -1 for silicalite-1 and -32 kJ.mol -1 .molec. -1 for chabazite upon condendation, at a much lower pressure than for defect-free zeolites. Hence, the water-water inter- action energy is dominant in the condensation mechanism and results in total energy -40 kJ.mol -1 .molec. -1 which is close to the bulk liquid value. The snapshots of water intrusion in silicalite-1 containing one weak defect per cell (see Figure ) confirm that condensation of water occur through rather homogeneous nucleation of water molecules, followed by a collapse of the water cluster into the bulk phase, as for defect-free silicalite-1. In presence of strong defects, however, the picture is drastically changed and the isotherms progressively transition from type V to type IV (Figure ). This evolution observed for silicalite-1 is in agreement with previous studies: There is some water uptake at low pressure and the transition is less sharp when the defect content is increased. When strong defects are present, the water-zeolite interaction becomes the dominant factor in the con- densation process as it becomes larger than the bulk cohesion energy of water at very low pressure. In that case, nucleation of water happens more heterogeneously at low pressure, around the defect sites, and each of these small water clusters acts as a seed in the condensation at higher pressure. This is shown by MC snapshots illustrating the heterogeneous nature of water condensation for silicalite-1 around the strong defects (Figure ). The type IV nature of the observed isotherms is thus explained by favorable adsorption of a moderate amount of water around the strong defects, followed by a sudden filling of the nanoporous volume. The effect of various type of silanol defects on water intrusion in silicalite-1 and chabazite are in qualitative agreement with previous studies focused on silicalite-1. 11,45