I really can't say anything about that myself, I'm really just using what I know on paper. Haven't really ubmerged a comp in liquid, and probably won't for a long long time. I'm scared to even use watercooling at this moment.
A word on watercooling: I think its the best cooling solution ever! If only they'd invent something as good as water that doesn't conduct electricity. Everything I mentioned up there has a problem: alcohol can't absorb alot of heat, oils degrade in heat, and if they don't, they're pretty viscous, and petrol is pretty much an oil anyway.
The CPU is the main heat producer (and lately the GPU is catching up) and whats better than whisking the heat away outside the casing and releasing it there, away from other components? Now they just gotta come up with waterooling for HDDs....
One thing about this "ultra pure water", its easy to obtain outside labs. All you need is to run a pipe through a bucket of cold water, boil water and lead the steam into that pipe (with a funnel) and what comes out the other end is pure water. Make sure that pipe is clean inside, and the initial streams of water is probably unpure, so let that drain. After that, assuming you've cleaned that pipe (or tube I should say), you'd have 99% pure water. Depending on how you handle that water will determine how long it'll stay pure

. Leave it in the air, and it'll go unpure pretty fast.
One more thing people can do to prevent water from totally destroying computers will be to coat everything in a little grease. Tehre's some special grease available in electronic shops which can be spread over electronics to protect anything from a little water for awhile. should be long enough for you to detect the leak and start cleaning up procedures. Not really sure if its good for leaks, but its good enough for creating a barrier for ice (I was looking into peltiers if anyone had followed my posts).