Some of you are saying, "Well, duh, they store water in the fat!" and it's true that when camels metabolize all that fat in their humps, they actually yield some water. But the yielded water is lost in the body, and the camel never gets to use it for nourishment.
But Cracked, you say, don't camels need water so they don't dehydrate? Well, yes, of course. But camels work differently from people. Camels can cool down, and stay cool, much longer than we can. They also have special cells that don't allow blood pressure to drop when body volume drops. All of it adds up to a creature that can go a long time without dehydrating.
They're like hardcore metal fans.
So How'd It Get Started?
The origin of this myth is probably twofold. Ancient Roman philosopher/naturalist Pliny the Elder is recorded as having hypothesized that a camel has two stomachs: one made to hold water, and another to hold food. The community at large accepted this as fact, and assumed that those two stomachs must be in the two humps.
There are also stories (which may have inspired Pliny) that say that traveling Muslim armies would split open a camel's belly and drink its water. Well, that's likely because food and water divide into two separate sections of the camel's stomach before digestion, allowing one to get a hold of the portion of the stomach filled only with water. Nomads in the desert are also known to drain water from half-digested camel food in times of desperation. Still, none of this adds up to the "water in humps" story we were all told.
It's like the tauntaun Han Solo killed in The Empire Strikes Back, only you can drink from it as well as live in it.