  The packing order of molecules and the distance between adjacent oxygen atoms
(dOO) in water and ice are most basic yet puzzling. Here we present a scaling
solution for this purpose based only on the mass density (gcm-3), (Equation)
where dL is the length ({\AA}) of the O:H van der Waals bond and dH the H-O
polar-covalent bond projecting on the O---O line. Validated by the measured
proton symmetrization of compressed ice, dOO of water and ice, and dOO
expansion at water surface, this solution confirms that the fluctuated,
tetrahedrally-coordinated structure is unique for water ice.
