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We report quartz crystal microbalance (QCM) measurements of the room temperature uptake of water by thin (<1μm) organic films. The mass of water taken up by films of dodecane, 1-octanol, octanoic acid, 1,5-pentanediol, 1,8-octanediol and malonic acid was measured as a function of the ambient relative humidity (RH). All compounds tested here displayed some sorption of water. Uptake by dodecane is probably due to surface adsorption; in the other films, water dissolves into the film material. Malonic acid and 1,8 octanediol show deliquescence-like behaviour at relative humitidies near 72% and 95%, respectively. In general, the higher the oxidation state of the film compound, the greater is the amount of water sorbed. An absorptive partitioning model, using UNIFAC calculations of activity coefficients, yields semiquantitative agreement with the experimental results at low relative humidities for all compounds …