I will try to be more constructive. Below is a qualitative energy diagram for high and low density water. The (a) is the high density and the (b) is low density. The difference is the high density (a) has a higher degree of nondirectional van der Waals and electrostatic interaction, while the low density (b) has a higher degree of directionality due to more directional partial covalent bonding character. The partial covalent bond separates the water molecules for better orbital overlap and reduces the number of water molecules that are in contact to a maximum of four, although it can also be less. The small potential energy barrier allows normal thermal affects to shift between the two easily so both zones will be found in water.
Here is my theory. The way I explain this is due to a tug of war between oxygen and hydrogen. An isolated water molecule has hydrogen attached to a highly electronegative atom. The electron density sharing stabilizes the oxygen but also creates a dipole. As we start the process the net burden of potential is on the hydrogen. At (a) the hydrogen is able to lower its potential better by sneaking around the oxygen, sharing as much electron density as possible by increasing density. Although this is great for hydrogen it will increase the potential of the oxygen. In (b) the oxygen does not take this lying down. Instead, it asserts its higher electronegativity forcing the hydrogen into more directed partial covalent bonds. This is energetically better for the system since the oxygen is more electronegative and gets its rightful share. But this sends some of the burden back to hydrogen. The hydrogen, in turn, with the help of a little thermal energy, tries to go back to (a). There is a constant tug of war.
An interesting tidbit is although we define water as H2O, in the liquid state this molecule will exist for about a milli-second. The covalent bonds are breaking and reforming due to proton-deprotonation type processes sort of mediated by hydrogen bonding. Again, this is the tug of war between oxygen and hydrogen, the oxygen is trying to assert its higher electronegativity and hog the electrons, while little hydrogen is looking for a better deal.
Water molecule structure