How Can a Camel Walk for Days Without Drinking?
The Hump Holds Fat, Not Water
Many people have heard that a camel's hump stores water. In fact, this is a common myth. The hump is filled not with water but mostly with fat. So how does a camel keep walking across the desert for days without a drink?
Plenty of people imagine a camel carrying water in its hump, like a canteen. But when the hump is examined, what's inside is not water but fatty tissue.
If the hump is not a water tank, how does a camel get through long spells without drinking? The answer is thought to be several mechanisms working together, a whole-body strategy.
When the fat stored in the hump is broken down in the body, water is made as a by-product.
Its body copes with big swings in temperature, so it is thought to hold back on the water lost through sweat.
Let's look at "water from fat" and "less sweating" one at a time.
The Hump Holds Fat, Not Water
A camel's hump is thought to be a raised mound of fatty tissue. It does not store water. The fat is thought to be stored as an energy source for times when food is scarce. "Hump = water tank" is a well-known picture, but it is a common myth that doesn't match how the animal really works.
Breaking Down Fat Makes Water: How Metabolic Water Works
When fat is broken down in the body (when breathing lets fat combine with oxygen and turn into energy), water is made as a by-product. This water is called "metabolic water". Because a camel stores a great deal of fat in its hump, breaking it down is thought to yield a good amount of metabolic water. This is one clue to how camels get through long periods without drinking.
It is a "fuel tank" that can make water when it is needed.
Temperature Control That Saves Sweat
Many animals sweat to cool down so that their body temperature doesn't climb too high. A camel, however, is thought to tolerate large swings in body temperature over a single day. It keeps its temperature low in the morning, and as the day heats up it is thought not to force itself to sweat and cool down, even if its temperature rises a little. Sweating costs the body water, so this tolerance for temperature swings is thought to save a lot of water.
A camel's kidneys are thought to be able to reclaim almost all the water in urine and produce very concentrated urine. The complex structure inside its nose is also thought to win back some of the moisture in the air it breathes out. During long stretches without water, savings are made all over the body.
Try It Yourself
- Dab a little water on the inside of one arm.
- Leave the other arm as it is, with nothing on it.
- Blow air on both arms in the same way, with a fan fanned by hand or an electric fan.
- Check that the arm with water feels cooler.
You can feel how sweat (evaporating water) cools the body. A camel, which makes little use of this cooling, is thought to save water that way.
Summary
A camel can go for days without drinking, but not because it stores water in its hump. It is thought to be the result of several things combined: metabolic water from breaking down hump fat, less sweating by tolerating temperature swings, and thorough water-saving by the kidneys and nose.
A camel's hump is not a water piggy bank. It is an excellent energy store that can even make water when it is needed.
So how much water do we humans lose in a day, without the camel's tricks? The article here explains, through the body's water balance, why emergency water supplies are set at "3 litres per person per day".
Plants living in dry places face the same challenge. To see how plants in arid land protect their water, read Why Don't Cacti Die Without Watering?
For Those Who Want More: Terms, Numbers and Links to TextbooksFrom middle-school science to active research, each part is labelled with its level
- Middle schoolCovered in middle-school science
- High schoolCovered in high-school basic biology
- High school+High-school advanced biology, or textbook extension and sidebar material
- UniversityUniversity-level specialist content (physiology), not taught in high school
- ResearchTopics researchers are still investigating, not yet taught even at university as settled fact
Middle schoolTerms: Words Around How Camels Keep Water
- Metabolic water: water made when fat and similar substances are broken down in the body.
- Temperature regulation: the body's effort to keep its temperature within a certain range.
- Reabsorption: taking water back into the body before it becomes urine.
High schoolChecking with a Formula: How Much Water Does Breaking Down Fat Make?
Let's calculate how much water fat breakdown produces, using a rough ratio.
| In symbols | W = m × 1.1 (W is the amount of water made, m is the amount of fat broken down; both in grams) |
| In words | Water made = fat broken down × 1.1 |
| Where it comes from | It comes from the reaction in which fat combines with oxygen and turns into carbon dioxide and water. A fat molecule contains a fixed number of hydrogen atoms, so the amount of water made from one gram of fat is fixed too. The water made inside the body this way is called metabolic water. |
Water made (g) = fat broken down (g) × 1.1 (rough ratio)
| The ratio 1.1 | A value taken as a rough guide to the water made when fat is broken down |
| Water made (g) | 50000 × 1.1 ＝ 55000 |
| Convert to litres | 55000 ÷ 1000 ＝ 55 |
| Result | About 55 L of water is made |
This is only a rough figure for the case where all the fat is broken down. In reality, fat is also used as energy for movement, so metabolic water alone is thought not to cover all the water a camel needs. Even so, given how much fat the hump holds, we can see that the body can make a good amount of water.
* The ratio "1.1" and the amount of fat are rough values to help explain the mechanism. Real values are thought to vary with the individual animal and the situation.
High school+Allowing Temperature Swings: An Energy Strategy
Sweating is a sure way to cool down, but it has a drawback: it uses up a lot of water. A camel's wide tolerance for temperature swings is thought to be a strategy that puts water first: "let the temperature rise a little rather than spend water".
UniversitySqueezing Out Water in the Kidneys
In physiology, researchers study how the camel kidney's special structure and function let it concentrate urine to a very high level. Camels are also known to have specially shaped red blood cells, which help keep the blood in good condition even as dehydration sets in.
This concentration of urine is thought to come from a system called the "countercurrent multiplier" working in the loop of Henle in the kidney. The water made when fat is broken down is called "metabolic water", and in other desert animals besides camels it also makes up part of the water balance.
📖 More detail, and further reading: Wikipedia (English), "Countercurrent exchange" / Wikipedia (English), "Metabolic water"
ResearchWhat Is Still Unclear
- How the range of tolerated temperature swings is fine-tuned is a topic still being studied in physiology.
- How the lives of dry-land animals like camels will change as climate change and desertification advance is also an important research question in ecology.
- Researchers are also exploring whether the camel's water-keeping mechanisms could be applied to treating human dehydration, or to farming and livestock methods in dry regions.
The body of a camel crossing the desert holds a rich subject, where physiology and ecology meet and research is still under way.
Links to Textbooks (by Level)
| Level | Subject / unit | Where in this article |
|---|---|---|
| Middle school | Science: respiration and metabolism | Basic terms: metabolic water, temperature regulation, reabsorption |
| High school | Basic biology: respiration and energy | Calculating the water made by breaking down fat |
| High school+ | Biology: homeostasis (advanced) | The energy strategy of tolerating temperature swings |
| University | Physiology | Water reabsorption in the kidney and specialised red blood cells |
| Research | Physiology and ecology (under study) | Detailed mechanisms of temperature control, effects of climate change, applied research |
- Explanations of metabolic water and fat breakdown in biology textbooks and reference materials.
- Explanations of camel temperature regulation and reduced sweating in physiology materials.
- Research reviews on water reabsorption in the camel kidney, from the field of physiology.
- Explanations of the shape of camel red blood cells in zoology materials.
- Research reviews on water-keeping strategies of dry-region animals, from the field of ecology.
* Figures such as the metabolic water ratio and the amount of fat are rough values to help explain the mechanism. Real values are thought to vary with the individual animal and environmental conditions.
* This article is a general science explainer. If you go to observe real animals, please follow the facility's rules so that the animals are not stressed.