The effect of a soluble surfactant adsorption layer on the water evaporation was studied using an osmometric method. It was proved that Knauer’s osmometer after appropriate modification of the measuring cell can be successfully used for a qualitative detection of the evaporation retardation, The osmometric behavior of the system was explained taking into account the adsorption properties of the surfactants and the heat effects accompanying the evaporation process, A measurable evaporation hindrance was registered only in case of sodium salts of myristic and palmitic acids at concentrations (close to the solubility limit) at which densely packed adsorption layers are formed, At the same time the latent heat of evaporation may cause a freezing of the higher density adsorption layer which is formed on the supersaturated solution drop.