A camel's hump stores fat, not water — the myth mattered enough to actually test

The common assumption is that a camel's hump is a built-in water tank, but it's actually fatty tissue, up to 36 kilograms of it, metabolised for energy when food is scarce. Physiologist Knut Schmidt-Nielsen's desert expeditions found camels survive dehydration through other means instead: minimal sweating, oval red blood cells, and tolerating water loss that would kill most mammals. Metabolising the fat does yield a little water as a byproduct, nowhere near enough to count as a canteen.

— Knut Schmidt-Nielsen, Desert Animals: Physiological Problems of Heat and Water — Oxford University Press, 1964