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Permeation of water in a poorly wettable material results in a conversion of pressure/volume work into surface free energy representing a novel form of energy storage. The addition of salt increases the amount of stored energy and can reduce the hysteresis of the infiltration−expulsion cycle. Our molecular simulations provide a theoretical perspective into the mechanisms involved in the process and underlying structures and interactions in compressed nanoconfined solutions. We consider aqueous NaCl in nanosized confinements at pressures of up to 3 kbar. Open ensemble Monte Carlo simulations utilizing fractional exchanges of molecules for efficient addition−removal of ions have been utilized in conjunction with pressure-dependent chemical potentials to model bulk phases under pressure. Confinements open to these pressurized bulk, aqueous electrolyte phases show reversibility at narrow pore sizes and irreversibility in wider ones, consistent with experiment. The addition of salt increases in the solid−liquid interfacial tension in narrower pores and associated infiltration and expulsion pressures. These changes are consistent with strong desalination effects at the lower pore size observed irrespective of external pressure and initial concentration.