Experimental investigations on the dewatering of ionic liquids (IL) in a single falling film evaporator were carried out. Depending on the process conditions, such as heating temperature and process pressure, a minimum water content of 0.2 wt‐% (2000 ppm) was achieved using batch mode. Assuming that these water contents represent equilibrium state at constant temperatures and pressures, vapor pressure curves of different IL‐water mixtures were obtained and from these the required heat for evaporation could be estimated. During the dewatering process viscosity was monitored online and proved to be a sufficient and reliable indicator for dewatering progress.