Chemical shifts (delta) in the H-1 NMR spectra of free water and water adsorbed onto fumed silica, silicalite, and fumed silica/alumina were analyzed using ab initio calculations and experimental data. Nearly linear relationships between isotropic delta(H,iso) values and the atomic charge of H (q(H)), the valence (r(OH)) and hydrogen (r(O ... H)) bond lengths, and the angle angle O-H ... O were found from the theoretical calculations bf the NMR spectra of free and adsorbed water. An estimation of delta(H,iso) for large water clusters involving several tens of molecules or relatively large oxide fragments was performed using the calibrated function delta(H)(q(H)) obtained on the basis of the ab initio quantum chemical studies of small clusters and the PM3 calculations of both small and large ones.