Question

As liquid water freezes, the molecules take up more space than liquid water. What do you think would happen if frozen water molecules required less space than liquid water molecules?

Answer 1

When an object changes from liquid to solid, and if the molecules in that solid object take up less state [in the solid as opposed to the liquid state], the solid object will sink rather than float.

Answer 2

Well, sailors would be safer, for one.
*Clears throat* Let me explain.
If frozen water molecules required less space than liquid water molecules, icebergs would probably sink. Yep, that's right. Then, the ocean would freeze over.
No kidding. :)