We have computed the torsional tunneling barriers for water molecules bound to actinyl ions, UO22+, NpO2+, and PuO22+ using high-level relativistic computations in aqueous solution. We show that the barriers drop substantially as a function of number of water molecules, which could assist facile exchange of water molecules from the solvent to the complex. Our findings are consistent with the O-17 dynamical NMR studies of Farkas et al. (c) 2006 Elsevier B.V. All rights reserved.