This work reports experimental results of the water uptake of Aerosol-OT (AOT) reverse micelles measured at several initial AOT concentrations, several concentrations of single and mixed salts in the aqueous phase, and several initial volume ratios of organic to aqueous phase. Due to the ion exchange between the cations in the aqueous phase and the sodium as surfactant counterion, the water uptake is strongly affected by the nature and concentration of the cations and it is insensitive to the nature of the anions, A model has been developed in terms of dimensionless groups using as input the initial conditions of the system. This model accurately represents the effect of the variables on the water uptake.