Accurate counterpoise-corrected SCF + MP2 total and partitioned interaction energies are reported at ten stationary points on the water-dimer potential energy surface. For further analysis, separate energy components were obtained using symmetry-adapted perturbation theory (SAPT). An interaction optimized basis set (IOM) of 136 functions was employed. At the global equilibrium geometry the binding energy for this basis is 1 kJ mol−1 less than the value at the basis set limit, but the relative energies at the remaining stationary geometries are much more precise. The new IOM data have been used to test the quality of several water–water potentials including SIBFA, ASP-W4, TAP, SAPT-5s and SAPT-5st. Focussing on the relative energies with respect to that of the global minimum, the r.m.s. deviations from the IOM data are found to vary from 0.4 to 3.5 kJ mol−1, those of the SAPT-5s(t) potentials being much the smallest. Inspection of the separate components of the SAPT-5s(t) potentials shows, however, that their components do not properly reflect the physics of the interaction, due to shortcomings in the chosen functional forms. It is suggested that a combination of successful ingredients of the various potentials may yield a water potential that is fairly simple, transferable to larger water clusters and yet more accurate than those currently available.