A camel hump is not used for water storage, but camels can go for long periods of time without water. They drink large amounts of water up to 20 gallons at a time. This water is stored in the animal’s bloodstream.
Camel hump actually stores fat.
The camel uses it as nourishment when food is scarce. If a camel uses the fat inside the hump, the hump will become limp and droop down. With proper food and rest the hump will return to normal.
The humps are actually reservoirs of fatty tissue: concentrating body fat in their humps minimizes the insulating effect fat would have if distributed over the rest of their bodies, helping camels survive in hot climates. When this tissue is metabolized, it yields more than one gram of water for every gram of fat processed. This fat metabolization, while releasing energy, causes water to evaporate from the lungs during respiration (as oxygen is required for the metabolic process): overall, there is a net decrease in water.