When the water freezes need line up in a particular pattern of the molecules. Because they have the shape of V this pattern really takes up a lot of space. Compare this to liquid water, where chaotic arrangement, moving constantly, allow the water to better “fill the holes”.
Water is quite special because it Is the relative abundance of hydrogen bond on the outside. On “normal” temperatures in liquid form, the water molecules bouncing much hydrogen bonds and a little “squishy.” Thus, as a whole, closer together, because they are all wringing their hands around each other. (Side note, since they are still bond, and hydrogen atoms are doing a lot of strange flopping around and attract each other, that is why there is liquid water cohesion and can form small droplets, or get sucked plants).
All energy and making the molecules bounce around when cold water, getting lower and lower, therefore, water acts “normal” come denser and closer together, until about 4 degrees c. below which is when water reaches strange. When energy/temperature is too low, it is not enough to make the movement of molecules hydrogen bond strength of suppression. So on that point that hydrogen bonds-shaped external all take over, all gaps separate molecules, pushing away from each other because of the payments associated with bonds.
A settlement would otherwise normally in space is slightly further apart than the molecules. They actually even slightly further apart than the molecules in when they are at room temperature. So in the end ice less dense than water, and floats.
Other facts, the width-related, but sort of related because it highlights how cold and essential water is life: the hydrogen bonds, as I mentioned, is responsible for “Save” water to other water. So plants can move water through their stems, roots leaves. As the water evaporates from leaves, the water chain a little light can be seen along, continually moving up “sticky” like a little conveyor belt sticky water. This leaves to all life as we know it happens.
Also, imagine a world where there were more intense than the liquid water frozen water. When ice forms on the surface, ice would sink. Then there would be more ice would form on the surface. And zinc. Repetition. It would not be able to support life freshwater lakes. Nothing but layers and layers of sunken ice for most of the year, or all forever. Maybe even the oceans only all ice, with sinking and forming ice caps all drainage water from the oceans continuously.