Supramolecular water dimer, (H2O)(2), is fundamentally important. During the course of our work on polyoxometalates, we have been able to identify the existence of hydrogen-bonded, near-linear water dimers in the "sinuous" channels of an inorganic framework material, Na-3n(H2O)(6n)[Al(OH)(6)Mo6O18](n).2nH(2)O, 1. The three-dimensional network structure of 1 in the solid state is assembled by the Anderson type of heteropolyanions as building blocks sharing sodium cations. Vibrational spectroscopy, X-ray powder diffraction technique, TG-DSC analyses, and single-crystal X-ray structure analysis have characterized this host-guest system, 1. Crystal data for 1: triclinic space group P (1) over bar, a = 12.0618 (3) Angstrom, b = 13.1570 (4) Angstrom, c = 14.1563 (4) Angstrom, alpha = 80.7850 (10)degrees, beta = 75.2660 (10)degrees, gamma = 68.9210 (10)degrees, and Z = 3.