Left panel: structure of water ices in a 4 × 4 × 4 grid. Each knot represent the position of an oxygen atom with odd vertical coordinates (yellow) and with even vertical coordinates (blue). This box illustrates the possible positions of water molecules in our grid model. The grey lines show the tetrahedrons in our grid that are used to calculate surface and volume. Right panel: water molecules with odd vertical coordinates (yellow) can move in the grid following the yellow arrows, while water molecules with even coordinates (blue) can move in the grid following the blue arrows.