Who was the first human being to drink the first gulp of water?

Fermented beverages have been around since the hunter/gatherer days of humanity's ancestors. While males were out looking for walking protein to eat, females stayed in the vicinity of the living territory and collected local vegetation to add to the diet. If it was plentiful, it might be stored in a skull or other convenient receptacle whereupon local bacteria would get to work on it and cause it to ferment. The lucky person that got to drink any liquid that resulted from overextended storage without refrigeration might get the world's first "buzz".

This, however may not have been the first instance of alcohol existing. Even today alcohol commonly forms around the bottom of grain silos if conditions aren't maintained correctly within. I've seen pigs staggering around from lapping up the liquid draining from the bottom of a grain silo.

This could very well have happened in nature with a bountiful crop of berries falling off a bush, fermenting naturally then being eaten by some hapless animal. So you're very unlikely to get the name of a "first person" unless you like the name "Unngh!"