Water ice has a crystalline structure that is unusual in several ways. The oxygen of each water molecule is equidistant from the oxygen of each of its four nearest neighbors. The oxygen atoms may be divided into horizontal planes in which the atoms are arrayed at the vertices of a regular hexagonal pattern in the plane but with neighboring atoms alternately a little above and below the plane. There is just one hydrogen atom between two of the neighboring oxygen atoms. The hexagons of adjacent planes are aligned except that the alternation is reversed. An oxygen atom thus has three other neighbors in its own plane and just one more from either the plane above or below.

The water molecule retains its integrity in ice. Each oxygen is attached to two hydrogens with a strong bond. It is also near two hydrogens of two other neighboring oxygens. Between each pair of neighboring oxygen atoms is just one hydrogen atom which has a short strong bond with one of the oxygens, and a weak longer bond with the other. There are a great many ways that a neighborhood of oxygen atoms can share their hydrogen atoms in this scheme. The number of ways goes up exponentially with the number of molecules. The constant factor in the exponent bears on the specific heat of ice.

According to this picture cubic ice has two populations of molecules. The oxygens of population 1 occupies each point whose coordinates are all integers and also each point with one integral and two half integral (n+1/2) values.

The oxygens of population 2 are displaced by the vector [1/4, 1/4, 1/4].

The oxygen at [0, 0, 0] thus has 4 population 2 neighbors at [1/4, 1/4, 1/4], [1/4, −1/4, −1/4], [−1/4, 1/4, −1/4] and [−1/4, −1/4, 1/4].

As in hexagonal ice there is one hydrogen between any two neighboring oxygens but it belongs to just one of them.

Unlike hexagonal ice the angle of the molecule is arccos(−1/3)=109.5⁰, which is good but not really what water wants, 104.4⁰. Hexagonal ice has fewer symmetries and thus enough latitude to make its angles just what it wants.

The oxygens in cubic ice are located like carbon atoms in diamond. There is a scale factor of 4 in the description.

See this and this about other forms of Ice and this about phases of water in general.