Monohydrated and dihydrated adenine-thymine base pairs are characterized using metahybrid density functional theory and correlated ab initio approaches. The motivation of this work is twofold. First, the high-level geometries and interaction energies computed for different complexes serve as a reference for the testing of recently developed density functional theory (DFT) with respect to its ability to correctly describe the balance between the electrostatic and the dispersion contributions that bind these complexes. Second, these studies of nucleic acid base pairs are important for finding binding sites of water molecules around bases and for a better understanding of the influence of the solvent on the stability of the structure of DNA duplexes.