Here's why:

* Water expands when it freezes. This is why ice floats! The molecules in ice arrange themselves in a crystal lattice structure, which takes up more space than the more loosely packed molecules in liquid water.

* Density: This difference in structure means ice has a lower density than liquid water. Density is a measure of how much mass is packed into a given volume.

In summary: It takes *more* space to hold the same amount of water in its solid form (ice) compared to its liquid form.