Camels are also known as 'ships-of-the-desert' as they can carry heavy loads around. It is not their ability to go without water for long periods that sets them apart, but the ways in which they cope with the harsh environment of the desert that does.
Coming back to their humps, camels store 'fat' in them, not water. The humps are emergency food reserves that are used in the case of food scarcity. In fact, baby camels do not have a hump, as the layer of fat doesn't develop till they begin to eat solid food.
So how exactly do camels take care of their water requirements? Or do they survive without water?
Camels do store water, but not in their humps. Instead, they store it in their body fluids, including their blood. Camels can drink up to 200 liters (52.84 gallons) of water at a time. They are quick drinkers, drinking 100 liters (26.4 gallons) of water in about 10 minutes. Additionally, they are not very choosy when it comes to the water, and are known to drink brackish or salt water as well. This along with their amazing ability to minimize water loss helps them survive without drinking water.
Unlike most warm-blooded creatures, which maintain a constant body temperature, a camel's body temperature changes as per the external temperature. It varies between 35°C (95°F) to above 40°C (104°F). This helps them to minimize water loss due to sweating as the temperature rises. They also have an unusual ability to avoid dehydration. While most animals would die of dehydration on losing 20 percent of their body weight in water (excessive loss of body temperature causes thickening of blood, which is almost always fatal), camels can survive even after losing up to 40 percent of their body weight.
In case you are wondering why the fat is stored only in the hump and not elsewhere, it is because fat acts as an insulating material and prevents heat loss. In the extreme conditions in deserts, camels need to lose heat freely, so instead of having a layer of fat all around, it is stored in a hump, leaving the rest of the body to freely lose heat.
While Dromedary camels have a single hump, Bactrian camels have two. Hence, they are referred to as the one-humped and two-humped camels respectively.
As a species, camels are perfectly adapted to survive in the desert. Each and every part of their body is customized for desert life. Winds in the desert often blow sand into the air, but the camel's long, thick eyelashes protect their eyes from the sand. If some sand does manage to evade their eyelashes, camels have a third eyelid to get rid of the sand; this extra eyelid moves from side to side like a windshield wiper and wipes the sand away. The third eyelid being very thin, camels can easily see through it. They can thus close this eyelid during a sandstorm and still see; in effect, they can actually walk with their eyes closed.
Additionally, camels have hair inside their ears to block sand and also have the ability to close their nostrils to keep the sand out. Their broad feet help them to walk on sand without sinking in it. Parts of the body that touch the hot sand when sitting, such as their knees, are toughened or callused. Camels have thick lips and tough lining in their mouth and thus, they can eat parts of plants that other animals can't. These includes the thorns of the acacia―a typical African savannah tree covered with long needles―as well. Interestingly, they are careful enough to eat only a few leaves from each tree, so as to not leave the trees completely bare.
Even in this mechanical age, camels are considered a strong and reliable means of transport in the desert. Besides transportation, they are a valuable source of milk and meat; their skin is used to make containers for carrying water, their manure as fuel, and wool to knit rugs and tents. No wonder the 'Bedouins' (Nomadic Arabs) call the camels 'Ata Allah' or 'the gift of God'.