The interpretation of the experimental self-diffusion data on normal and supercooled water has been revisited in the light of both the recently reported evidence for a temperature-dependent H-bond cooperativity and the free-volume fluctuations within the water percolative patches. The proposed model, which is consistent with the presence of a continuity of states between liquid and solid phases, was found to fit the NMR experimental data to an accuracy comparable to that obtained by a power law.