Mixtures of ionic liquids and water offer an interesting opportunity to replace corrosive and/or partly miscible working pairs like lithium bromide water in absorption chillers. Such an alternative must feature both a high depression of the water vapor pressure and a low viscosity to be feasible. However, hitherto published literature data of binary systems of ionic liquids and water fulfill only one of the two criteria. A mixture of two different ionic liquids may exhibit a solution for this dilemma. In this work, a ternary system consisting of water, 1-ethyl-3-methylimidazolium acetate ([EMIm][OAc], high reduction of vapor pressure), and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMInn][OTf], low viscosity) was investigated. Experimental data for density, dynamic viscosity, and vapor liquid equilibrium in the temperature range from 293.15 to 353.15 K at water mass fractions between 5% and 20% and different mass fractions of [EMIrn] [OTf] are presented. The viscosity of the ternary mixture measured with a falling ball viscometer range between 90.9 and 1.9 mPa.s at a relative mean deviation below 3.6%. The density measured with a glass pycnometer range between 1087 and 1285 kg.m(-3) at a relative mean deviation of 0.33%. The water vapor pressure measured by infrared spectroscopy range between 293 and 15164 Pa. The relative mean deviation is below 15.1%. The water vapor pressure data are correlated using a nonrandom two liquid model. The thermodynamic properties show that the considered ternary system can indeed be used as a suitable working mixture in absorption refrigerators.