Ex-Army infantry guy here.

In basic training, location Ft. Benning GA, late August. Hydration was important, and that was impressed upon us by the drill sergeants, who would pause the activity at hand for the moment and do the 'Drink Water!' call, to which we'd reply mostly in uninspired enthusiasm 'Beat the heat drill sergeant beat the heat.'

We'd then down a canteen (a quart) of water. On especially hot days, we'd do two canteens. No dumping on your head or on the ground - you had to finish one or both. We'd refill canteens and get back to the day's task of doing push-ups, sit-ups, crunches, and in-between those, learning Army stuff (sir).

One guy, Peterson (name changed), couldn't do a canteen of water. This guy was the opposite of Joey Chestnut. He ate and drank like a bird but never lost weight. Slow metabolism and high energy conversion I guess. He never seemed dehydrated I would say. But water and food were just minimal for the guy. He'd drink a pint, maybe a sip more, and done.

Our drill sergeants weren't having that. You had to finish the canteen and flip it over your head. Failure to comply was met with drinking more water, until you finished the canteen, while your platoon did push-ups. No pressure.

The rest of the story transpired really quickly.

The drill sergeants hit him with the order to drink more water, and he did, and he stopped, and then they said keep going private, and he was in obvious pain, and he said no drill sergeant, and you could see the crinkle in the eyes of the questioned, but before that drill sergeant's body language became verbal, Peterson puked up water, gallons of water it seemed, then breakfast, and the upper contents of his colon I'm pretty sure (j/k being illustrative). A medic, who just happened to be Starship Trooping on by, got on the horn and got the kid to a clinic. He was water intoxicated, we later found out.

One of the great things they forget to show you on the recruitment brochure lol. He was eventually fine, and we were relegated to drinking until we could spit out saliva a few inches.