Measurements of counterdiffusion of water, ethanol, and NaCl through several commercial ion exchange membranes have been conducted in the context of evaluating the suitability of using ethanol as the "draw" agent for forward-osmosis-based water recovery from highly "impaired" water sources. The water versus ethanol selectivity (ratio of permeances) was determined for a range initial water salinities (all greater than seawater) and ethanol mole fractions. Differential swelling at the two membrane interfaces provides for a maximum in the observed selectivity with respect to the relative driving forces. The transport is modeled with a classical solution-diffusion model with consideration of variations in the molar densities at the two interfaces.