A model is developed to predict the binding of counterions, or dissociation fraction of surfactant, at the reverse micellar interface. The model is based on the chemical equilibria between the counterions bound to head groups at the reverse micellar interface and the free counterions in the water pool. No adjustable parameter is used for the calculation of the dissociation fraction. The model is further extended to predict the water uptake. The extended model accurately represents the water content in the organic phase for both single and multiple salt systems.