Hey can I add something I am a chemistry major so I am not talking completely out of my ass. Most DI water is not dionized, and as everyone (err I mean all science majors) know water dissasociates into ions 10^(-14) is the dissasociation constant. MOst dionizers make the water acidic though, and it is corrosive. However it does not usually conduct b/c there is too few ions. Anyway I am going to get a water cooling rig soon too.
oh things wont grow in pure water either really, I mean obviously they need other stuff, light(duh), and dissolved gases. Of course you all know this to some extent I am sure.
I read a cool thing that 3M, sells (hydrofluoroether I think) and I am sure other companies sell similar products, it is a chemical, that you can immerse the computer in(not moving parts) so hard drives and what not have to be out, but usuing that in a cooling system would be cool. I read a thing where they did that (imerssed the computer,) and used liquid N2, to cool the fluid it was farily neat.