The water activity equilibration over saturated salt solutions was monitored in the ionic liquid 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide and in two organic solvents (methyl tert-butylether and n-hexane). Water uptake by the ionic liquid was comparable to that in polar organic solvents. Furthermore, the kinetic resolution of (R,S)-1-phenylethanol catalysed by a lipase from Pseudomonas sp. had a higher selectivity in the ionic liquid at low water activities (a(W)<0.53) than in methyl tert-butylether. At 60-90 &DEG;C E-values of about E&SIM;150 occured in the ionic liquid, while the enantioselectivity drops to values of 4 in methyl tert-butylether at the same temperatures.