Almost all of the chemical reactions required for life occur only when the relevant molecules are dissolved in water - it is not surprising then that our bodies are almost two thirds water. Since we consistently loose water through evaporation, urine, and other processes, we need to replace it with water we drink. Although we create a small amount of water through metabolic reactions, it is nowhere near enough to survive.

Animals which are adapted to live in drier climates are typically much more efficient with their water usage. In fact, some animals don't need to drink at all - they recuperate all of the water the loose through the metabolic breakdown of sugars.

About 50-80% of the human body is composed of water. The exact amount of water in the body varies according to age and the proportion of muscle-to-fat (muscle contains more water than fat.) Interestingly, we can survive for weeks without food, but only a matter of days without water (perhaps 3-4 depending on the conditions).

But what exactly does water do? It turns out that water plays a vital role in nearly every bodily function. Water is essential for digestion, nutrient absorption and chemical reactions. It is also essential in removing acidic waste from the body through the digestive tract. Water is also necessary for proper circulation in the body (as the plasma that carries our blood), and for the flexibility of the blood vessels themselves. Water is a key in helping us regulate our body temperature at or around 98.6 degrees F.

If our water level inside our body falls too low, we experience several symptoms that warn us we may be dehydrating. The principal symptom is thirst, a reaction influenced by a group of nerve cells located in the hypothalamus, located at the base of the brain. These symptoms occur to warn our body that it is experiencing Chronic Cellular Dehydration, a condition in which the body´s cells are under hydrated which causes them to weaken, leaving them vulnerable to disease. So always drink a lot of water!

We use water as a solvent. All of the chemistry that our bodies work on takes place in a liquid state, with molecules hopping around and getting where they need to go because they can be freely dissolved in this liquid. The liquid that we use is water. Thus, without it, our body chemistry can't happen, and we die.