Did not know that. Sounds like it's worth experimenting with before your test date. A few sips of water here and there would probably mitigate any major discomfort caused by the thirst. You're allowed a water bottle or something during the test I assume?
Then again, and I think someone mentioned this ITT already, high amounts of caffeine coupled with the natural adrenaline that will be pumping through your veins on test day might work against you. You can't emotionally simulate the actual day of your exam.
Caffeine doesn't actually make you hyper at normal dosages (that's the guarana and taurine), it just prevents melatonin from doing its job. The problem with too much caffeine is the diuretic effect. A diuretic and water will
make you pee; my statement about salt was more to indicate that there really isn't a practical way to counteract the effect.
I'll be taking a vitamin B based energy shot, as I mentioned earlier. It contains caffeine (lower dosage than say, Red Bull) and provides an energy boost that will stick around for 4-6 hours without the jitters. I hope to sneak in a few minutes of meditation before the test actually starts to settle down. I'm considering a couple other things, but not unless I can get a trial dose or two first.