Expansion valves.. If I am thinking of the right thing.. work best in refrigeration systems
You are so limited with cooling of water.. IT's either let it evaporate.. like in a bong setup.. or run it through a rad.. And it's no matter because the water can already take up so much.. Even if you were able to cool that water another 3C.. you probably wouldn't see a better overclock.. Probably just a more stable one..