In this work, we investigated the intrusion of electrolyte solutions in three representative hypothetical zeosils (silicalite-1, chabazite and faujasite) chosen for their increasing channel/cage diameter and the availability of experimental data. First, we calculated the isotherm of pure water intrusion by GCMC simulation in each of these three zeosils. Then, using the configurations of water-loaded zeolites at equilibrium at different pressures, we apply our osmostat and found that the alchemical work associated with ion insertion in the zeosils is much lower than in the bulk, leading to very low probabilities of intrusion.