Camels can go for days or even weeks with little or no food or water.
Most kinds of animals store fat in their bodies, but only camels keep most of their fat in a lump. If food is hard to find, the fat in the hump provides energy for the animal. If a camel is starving, its hump shrinks. The hump may even slip off the animal's back and hang down on its side. After the camel has had a few weeks' rest and food, its hump becomes firm and plump again. The hump is not a storage place for water, as many people believe.
Camels can flourish on the coarsest of sparse vegetation and feed on thorny plants, the leaves and twigs of shrubs, and dried grasses that other animals would refuse, though camels are not averse to better food if available. When the feeding is good, they accumulate in their humps stores of fat, which, when conditions are adverse, they are able to draw upon not only for sustenance but also for the manufacture of water by the oxidation of the fat.They thus are able to fast and go without drinking for several days; they have been known to go without water for 17 days and survive. They lose their body water slowly and can lose up to 25 percent of their weight by dehydration without ill effects. They can then regain their lost weight in a few minutes by drinking as much as 100 litres of water.
A camel needs little water each day because it gets some moisture from its food. Also, it keeps most of the water that is in its body. The amount of water a camel drinks varies with the time of year and with the weather. Camels need less water in winter when the weather is cool and the plants they eat contain more moisture than in summer. Camels that graze in the Sahara can go all winter without water and may refuse to drink if water is offered to them. But in very hot weather, a large, thirsty camel can drink up to 200 litres a day. This water is not stored in the camel's body but replaces water previously used up.