Ya I've been in the hospital before from drinking too much water. It all depends on how many salts & electrolytes your body has and is being replenished with. Your body needs them to survive and if you are passing them out faster than you are restoring them then you'll kill yourself. So if you regulate everything you can drink as much water as you'd like. This is why construction workers in Arizona usually take salt tablets as well as soldiers in places like Iraq.
I personally find 1 gallon a day plenty. It isn't too much but i get a great sweat at the gym, always clear piss, and i don't get crazy cramps when on a diet.
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