Why does water exhibit anomalous behavior near its freezing point?

[Badfish97]

So as some of you already probably know, water exhibits anomalous behavior when its temperature increases from 0°C to 4°C (it contracts) and when its temperature is decreased from 4°C to 0°C (it expands). Why does this happen?

 

[jajabinker]

When water is ice (0°C) it has a structure that has a lot of empty space in between, due to the low temperature and symmetrical hydrogen bonding.
http://www.uic.edu/classes/bios/bios100/lectures/02_15_hydrogen_bonding-L.jpg

In the liquid state there is a more irregular pattern for hydrogen bonding, but far from random.

As you decrease the temperature of a liquid,the density increases, for most materials. But as water goes below 4 degrees, there is a phase transition where these hollow structures form(like Ice 1h), which now reduce the average density of water.

 

[Badfish97]

When water is ice (0°C) it has a structure that has a lot of empty space in between, due to the low temperature and symmetrical hydrogen bonding.
http://www.uic.edu/classes/bios/bios100/lectures/02_15_hydrogen_bonding-L.jpg

In the liquid state there is a more irregular pattern for hydrogen bonding, but far from random.

As you decrease the temperature of a liquid,the density increases, for most materials. But as water goes below 4 degrees, there is a phase transition where these hollow structures form(like Ice 1h), which now reduce the average density of water.

So you're saying that when its temperature increases from zero degrees to 4 degrees, the irregularities in its hydrogen bonding increases, therefore it becomes denser?

 

[jajabinker]

Yes.
Let me show you a video
Notice how the black spaces disappear. i.e. more number of molecules per black space appear. Which is roughly your density.
This comes from molecular dynamics simulations. Great care has been taken over scores of work hours to ensure this is a realistic model.

Its rather intuitive.