How long can a human go without water?

Under excellent conditions, a human in decent physical shape can live up to five days without water, according to HowStuffWorks. A human in even better shape may survive another 24 hours or more.

One week appears to be the maximum length of time any human can go without water, an article in Business Insider says, and three or four days is a reasonable average. In extreme heat, a human cannot survive as long without water, and when temperatures are cool, a human can live somewhat longer. A person who is overly physically active in severe heat conditions can die in a few hours if he consumes no fluid, points out HowStuffWorks.