SCF ab initio computations of water-cation interactions are reported for Li+, Na+, K+, Mg++, Ca++, and NH4+ in view of exploring the utilizability (if any) of relatively small basis sets in this area. Starting with an STO 3G standard set on both the ligand and the cation, a careful scrutiny using a decomposition of the binding energy into its electrostatic, exchange, and delocalization components shows that the poor performance of this basis is due partly to the poor intrinsic representation it gives of the two entities, partly to the overavailability of empty orbitals on the ion. Successive improvements of the cation basis and of the water representation up to the 4–31G level are discussed in the same light and show that the performances of a split basis in this area can be surpassed by those of a good minimal set. General interrelations between the alkali and alkaline-earth ions are demonstrated in the light of the energy decompositions.