In computational chemistry, atomistic Monte Carlo (MC) simulations are routinely used to study the structure and equilibrium properties of condensed phases, solid or liquid, and their interfaces. Water is an important fluid in nature, and aqueous electrolytes at various concentrations are a key component of many chemical and biological systems, as well as used in applications such as batteries, desalination, and pollution remediation. Consequently, the insertion of ionic species in a dense fluid such as water is required for molecular simulation in many situations involving open systems, such as the osmotic equilibrium through membranes or the uptake of electrolytes in nanoporous materials. The Grand Canonical Monte Carlo (GCMC) simulation method is well-suited for simulating the molecular insertion or exchange of neutral species in fluid phases, and is used ubiquituously in the simulation of gas and liquid adsorption in porous materials. However, its use for ionic species is particularly inefficient: in addition to the fact that finding suitable cavities large enough in the fluid to accomodate ion insertion would appear infrequently, as for any large molecule, the strong organization of the solvent induced by the electric charge gives the insertion move a low probability. Secondly, electrical neutrality of the system imposes the insertion of pairs of charge-balancing ions (or more), which further decreases the probability of a successful Monte Carl insertion move.