Abstract The structures, interaction energies and proton transfer features of two water complexes, namely H 4O 2 and H 5O 2 +, have been determined using density functionals, which incorporate gradient corrections and some Hartree-Fock exchange. The method is validated by comparison with the available experimental data and with the results of sophisticated post-Hartree-Fock approaches. The new functional provides accurate structural, energetic, and spectroscopic properties at a fraction of the cost of conventional post-Hartree-Fock approaches giving similar accuracies. The improvement with respect to standard functionals is also significant, especially concerning OH and intermolecular OO distances. These, in turn, affect the computed proton transfer barriers, which are now much closer to those obtained by the most reliable theoretical approaches.