A computational study has been performed in order to characterize the interactions in ternary systems formed by an ion pair of ionic liquids (ILs): [C(1)mim(+)] [BF4-], [C(1)mim(+)] [NO3-] and [C(1)mim(+)][CF3COO ], and one water molecule. Using CCSD(T) values extrapolated to basis set limit as reference, the performance of six different functionals has been assessed giving the following order (from better to worse performance): M06-HF similar to M05-2X > M06-2X > B97D > PBE0 > B3LYP. The best functionals perform similarly to MP2/aug-cc-pVTZ, with mean absolute deviations around 0.7 kcal/mol, whereas PBE0 and B3LYP deviate by more than 2.0 kcal/ mol. (C) 2014 Elsevier B.V. All rights reserved.