Abstract: Nuclear magnetic resonance studies of the hydrated cobalt oxide superconductor NaxCoO2·1.3H2O are reviewed. The results indicate that line nodes are present in the gap function, and that the Cooper pairs are in the spin-singlet state. The antiferromagnetic spin correlations are found to play an important role in producing the superconductivity. The main effect of water intercalation is to produce antiferromagnetic spin correlations in addition to making the system more two-dimensional.