The systems we studied are three representative pure silica zeolites: silicalite-1 (MFI topology), chabazite (CHA topology) and faujasite (FAU topology). For channel-type zeosil such as silicalite-1, the intrusion pressure of water depends on the channel diameter d ch while for cage-like zeosils (chabazite and faujasite), it correlates with the cage diameter d ca . We have chosen these zeosils because of the increasing "characteristic diameter": in increasing order, silicalite-1 (d ch = 5.40 Å), chabazite (d ca = 7.37 Å) and faujasite (d ca = 11.24 Å). The zeosils are generally considered rigid and it is assumed that no structural or chemical changes occur upon electrolyte intrusion or extrusion. We used the crystal structure determined by Olson for silicalite-1, the chabazite structure is that reported by Calligaris 61 while faujasite structure is that published by Hriljac. Table : Cell parameters of zeosils used in this work. We note here that pure-silica faujasite has not been synthesized so far, and even experimental faujasites with high Si:Al ratios exhibit a significant number of aluminium atoms.