Water

Water is clearly the most important nutrient in the human body.  Water comprises about three quarters of the human mass and is a major component in every cell.  In addition water is important to human health for many reasons including but not limited to the following:

• Water is needed to separate (by a process called hydrolysis) a phosphate group from adenosine triphosphate (ATP) or guanosine triphosphate (GTP) to get energy as illustrated by the following equations.

ATP +H₂O = Energy + ADP + Inorganic Phosphate
GTP +H₂O = Energy + GDP + Inorganic Phosphate

Water is the containing medium for electrolytes and all other ions throughout the human body.

Some of these ions help to form electrical pathways for nerve functions.

Being 2% dehydrated can seriously degrade physical and mental functions.

Being 15% dehydrated is likely to be lethal.

Unlike vitamin deficiencies which can take weeks to make someone ill, a water deficiency can kill in days or even hours.

Water is also very important for removing toxins from the human body.  The body has four major ways of removing toxins which are:

Bowels
Urination
Perspiration
Processing of toxins by the liver

The first three of these four methods directly excrete water from the body.  When dehydrated, the body will try to save water by minimizing the use of the first three functions and will force the liver to assume as much of the workload as possible.  This extra work will place a heavy burden on the liver which still has other functions in addition to detoxification.  Even then, the liver by itself will not be able to do all that work very efficiently and toxins will build up rapidly. 

Water is also important to fitness and fat loss for several reasons including the following:

Water fills us up without adding any calories.
Dehydration will degrade a person’s ability to exercise and burn calories.
Dehydration will reduce protein synthesis which is needed to build or repair muscles.

It is normally recommended to drink about 2 to 3 quarts of water per day.  However, this will vary with the size and activity level of the person as well as with the climate conditions.  Either case, if your urine is bright yellow, then you need to drink more water.  Also, anyone who exercises nonstop for more than 1 hour should consider replacing electrolytes along with the water.  This is to avoid hyponatremia (depleted sodium) or other forms of severe electrolyte depletion which can be dangerous.