As a general rule 3 days without water you risk death. In theory you can survive 4-5 days assuming ideal circumstances (resting in a cool, shaded place) and immediate hospitalization upon rescue. Going 6 days without none would be able to work and everyone would die of kidney failure in the next few days that wasn't already dead. 7 days is a myth that comes from the fact this is how long it takes you to actually die, not how long someone can go and recover. Sorry I misremembered his claim being 10 days.
https://www.removeddit.com/r/IAmA/comments/4d67or/_/d1o4fp0/
(post is archived)