When I was little I heard the same thing every time I asked about Camels, “They store water in their humps because they live in the Desert.” It seemed reasonable, strange, but reasonable. Much like the lie about Taste Buds and brain usage, it stuck with me for decades unquestioned. I thought smugly from time to time about the ridiculous things lots of people believe and yet so many things I believe are lies.
I would later find out that the stumps store fat and again this is not for them to store water in. They will lose more water from pulling from their fat reserves than they gain. The camel is quite a complicated creature, having spent many generations of natural selection in its inhospitable climate.
Their blood is special and helps them retain water longer than they would if they had our blood. Their noses are miraculous little recyclers that also retain moisture. Additionally, and I’m glad I don’t suffer from this same fate, (though I suppose they aren’t suffering), their feces and urine are both considerably less water dense than yours or mine.
These traits, and incredible instincts, allow them to survive in lands that tend to eat up people the moment they put their guard down. You can learn all about the Camel over at Wikipedia, which I highly suggest. Heck, pick your favorite animal and read about it. You will almost always be surprised by what you find out.