Not sure if it's intended or not, but i think you can get "negative" thirst?
With zero food and zero water i ate a bunch of chips and tuna (-35 thirst total i think) and then 1 purified water, and the water barely got me mid-way through my thirst bar.
Tried it again and can confirm, ate 5 million chips bags and then purified water and it does seem like you get less. Also if you eat the food with negative thirst, leave the menu, then go back in to the menu and drink the water THEN water works correctly, almost as if if you leave the menu your -50 thirst get set back to 0