It is the most important liquid a person can drink.  Our bodies are 70% water.  The blood and the lymphatic system are over 90% water.  It's essential for your health that you drink only pure, uncontaminated water without inorganic minerals or toxins.  One needs to keep hydrated.  Water provides this where other liquids do not.  Caffine and alcohol are diuretics thus causing you to lose water that is so needed for proper bodily functions. 

How to compute the amout of water to drink in a day?  Divide you weight in half and that is the number of ounces.  However, one should try to drink a minimum of 64 oz should you weigh less than 128 lbs.