where we introduced the activity of water in the electrolyte solution a CnAm water being the ratio between P vap CnAm and P vap water . Equation is the analytical model used subsequently to predict the intrusion pressure of electrolyte solution in zeosils. In Figure , we select an hypothetical intrusion pressure P water of 1 MPa from the pure water reservoir and deduce using Equation that the corresponding intrusion pressure of water from the electrolyte solution reservoir leading to the same acceptation probabilities of water intrusion (Eqn. 5) is 33.5 MPa. This example shows qualitatively that a decrease of vapor pressure of a solution due to presence of electrolyte is consistent with a shift of intrusion pressure towards higher values. Our model requires as input the water activity in electrolyte solutions a CnAm water over a wide range of concentration in order to rationalize intrusion pressure of electrolyte solutions in zeosils. There has been a large effort in order to obtain thermodynamic data (osmotic coefficient, activity coefficients...) of electrolyte solutions, either acquired experimentally to build theoretical models or through molecular simulations. The most widespread computational technique is the Gibbs Ensemble Monte Carlo method based on particle exchange between two reservoirs containing the two phases in equilibrium (e.g. liquid and vapor phase for water). Unfortunately, Gibbs Ensemble Monte Carlo method in combination with the atomistic force field as used in our study make these simulations costly to predict precisely vapor pressure of electrolyte solutions. Another approach is the grand canonical screening technique used to determine the point of liquid-vapor coexistence for systems in contact with vacuum. The vapor pressure of LiCl and NaCl has been obtained from screening various chemical potential using GCMC simulations, but using a coarse-grained description of electrolyte solutions. Consequently, this approach has the same limitation as for the Gibbs Ensemble Monte Carlo method to be used in combination with atomistic force fields. Also, another straightforward approach used a modified Widom insertion Method 82 to compute the activity coefficient of electrolyte, but in implicit water solvation making it unsuitable for atomistic force field either. Theoretical models based on experimental thermodynamic data are alternative approaches to predict vapor pressure (and by extension activity of water) in electrolyte solutions. The Debye-Hückel theory provides analytical equations to calculate activity and osmostic coefficients, but its validity domains is about of ∼0.01 M because of the neglect of short range interactions, ion size and ion-ion correlations. There has been a huge effort devoted to extend the applicability range of the Debye-Hückel theory by adding the above effects through fitting parameters. Along this line, the specific interaction theory uses experimental equilibrium constant at different ionic strength to determine activity coefficients for a wide range of concentration. A more sophisticated model has been proposed by Pitzer 87 by which activity and osmotic coefficients of single as well as mixed electrolytes at different temperatures can be modeled up to molalities of ∼ 10 mol/Kg, at the expense of a higher number of fitting parameters. We decided to use the Pitzer model in our work, not only because it is a sophisticated model that has been widely used in the literature but it has has been extented for various electrolyte combinations and concentrations. The version 0.5.2 of the Pytzer simulation package is the state of the art summarizing the pitzer parameters available in the literature for the series of electrolytes used in this work.