In an earlier study [1], a surfactant layer at the interface between a cellulose acetate membrane and a saline solution in reverse osmosis was shown to act as a liquid membrane in series with the solid membrane gel. Inasmuch as the effectiveness of liquid membranes in increasing the perm selectivity of the underlying gelatinous membranes increased with increasing surfactant hydrophilicity, it was postulated that solute rejection was at least partially attributable to the water-binding capacity of the various surfactants. In the present study, spectrophotometric evidence for the existence of surfactant-water interactions is presented.