Through use of in situ Raman spectroscopy and single-crystal/powder X-ray diffraction, we resolve the "C-0" phase structure discovered recently in the H-2 + H2O system. This phase forms at similar to 400 MPa and 280 K with the nominal composition (H2O)(2)H-2 and three formula units per unit cell. The hexagonal structure is chiral, consisting of interpenetrating spiral chains of hydrogen-bonded water molecules and rotationally disordered H-2 molecules, and shows topological similarities with the mineral quartz. Like other clathrate hydrates and forms of ice, the protons of H2O molecules within C-0 are disordered. The large zeolite-like channels accommodate significant amounts of hydrogen (5.3% by weight) in a unique hydrogen-bonded lattice, which might be applicable to the thermodynamic conditions found on icy planetary bodies.