Answer:
When the water freezes a reticulum is formed that occupies more space and is less dense than liquid water since the water on cooling decreases its volume. The reason why the water is denser in a liquid state is because, when it goes to a solid state, the water molecules are cold and still and the hydrogen bonds keep them constantly at the same fixed distance, while when they are in a liquid state, their hydrogen bonds are not at a fixed distance, but more separated.
