Drinking eight glasses of water a day is believed by about three fourths of adults with no reliable clinical evidence to support it.
One study on this myth was conducted in 2002 by Heinz Valtin, a
Dartmouth Medical School physician and kidney specialist, who
researched the subject. He believed that the statement supporting
the eight glasses belief is taken from the Food and Nutrition Board
of the National Research Council. It grossly misrepresented the
facts by removing facts from the original context. The sentence that
followed it stated, “most of this quantity is contained in prepared
foods,” which was left out and led to the false interpretation that
the requirement needed to be fulfilled by drinking water alone.
After 45 years of studying the biological system that keeps the
water in our bodies in balance, Valtin concluded that drinking such
large amounts of water is not needed at all. He pointed out a number
of published experiments that attest to the capability of the human
body for maintaining proper water balance from sources other than
directly drinking water which may include drinks such as tea,
coffee, and soft drinks, as well as prepared foods.
Most foods have some water content. For example, apples: 85%, bean
sprouts: 92%, boiled chicken: 71%, raw cucumbers: 96%, lettuce: 96%,
potatoes: 85%, roast turkey: 62%, etc.
The bottom line is that the body lets us know when we need more
water by making us feel thirsty. People who have specific health
concerns, such as kidney stones or urinary tract infections require
drinking large amounts of water. Other reasons for drinking water,
such as before meals to curb an appetite is its own benefit.
Further scientific evidence also debunks the myth that by the time
you feel thirsty, you are already dehydrated. A number of scientific
studies have confirmed there is no support for this. Thirst hits
long before we are near risk for dehydration and most folks thirst
mechanism kicks in when the osmolality of the blood plasma is less
than 2%, and dehydration begins at osmolalities of 5% and higher. I'll
drink to that.