A recent suggestion that acetamide, CH3C(O)NH2, could be readily formed on water-ice grains by the acid induced addition of water across the C≡N bond has now been shown to be credible. Computational modeling of the reaction between R-CN (R = H, CH3) and a cluster of 32 molecules of water and one H3O+ proceeds catalytically to form first a hydroxy imine R-C(OH)═NH and second an amide R-C(O)NH2. Quantum mechanical tunneling, computed from small-curvature estimates, plays a key role in the rates of these reactions. This work represents the first reasonable effort to show, in general, how amides can be formed from nitriles and water, which are abundant substrates, reacting on a water-ice cluster containing catalytic amounts of hydrons in the interstellar medium with consequential implications toward the origins of life.