© J. Dirk Nies, Ph.D.
Water is the most important substance of life. To live, we must take it into our bodies; to thrive, we must lose it. To be alive, water must flow through us like a stream.
Water is our body’s principal chemical component, representing roughly 60 percent of our total body weight and three-fourths of the weight of our brains. Every physiological function and process that goes on within us depends on water. Our bodies must have water to digest our food, to carry out the myriad biochemical reactions that occur in our cells, and water is necessary to rid ourselves of toxins and waste. We need water within us to regulate body temperature, lubricate joints, moisten tissues, and carry nutrients and oxygen throughout our bodies. The list goes on and on.
Because we lose water constantly, if our intake is too low, over time, we will become dehydrated. (If we feel thirsty, we’re already a little dehydrated.) Not only our bodies but our minds will become stressed. For good health and proper bodily function, we must consume sufficient water to make up for losses that naturally occur through breathing, perspiration and excretion.
How much water does a healthy adult living in a temperate climate typically need each day? The Institute of Medicine (IOM) has determined that adequate fluid intake is around 90 ounces for women and 125 ounces for men. These guidelines are for total fluid intake.
Roughly three-fourths of our total water intake comes from drinking water and other beverages. Assuming this estimate is an accurate reflection of our diet, IOM recommendations correspond to a daily fluid intake of about 8 cups for women and 12 cups for men.
Food provides the rest of our total intake of water. For example, consuming fruits and vegetables, which contain copious amounts of water in proportion to their weight, provides hydration. To illustrate this, here are water content levels for some popular fresh fruits and vegetables: broccoli, cabbage, eggplant, lettuce, radishes, strawberries, tomatoes, watermelon and zucchini (92-95 percent); apples, apricots, blueberries, cherries, grapes, peaches, plums and raspberries (81-88%). Carrots (87%), peas and potatoes (both 79%) are among the least moist fresh vegetables; bananas (74%) are among the driest fresh fruits.
Water not only flows through us, it often stops along the way, biochemically transformed into new compounds. Its constituent atoms—hydrogen and oxygen—are used as raw materials by the fabricating machinery of life in the making of new substances. For example, during digestion, with the help of enzymes, protein is broken apart (hydrolyzed) by water into its constituent amino acids. As this happens, the atoms of water are incorporated into the structure of the freed amino acids that were formerly bound together.
In all of nature, water’s most important role as a raw material occurs during photosynthesis. Green plants capture energy from the sun to split apart water, freeing hydrogen atoms from their bonds with oxygen. These reactive hydrogens are used in conjunction with carbon dioxide obtained from the atmosphere to synthesize sugars. Only the hydrogens of water are used in this process. Oxygen is given off as a by-product, released to the atmosphere as a gas. With every breath we take, the life-giving oxygen we draw into our lungs was once part of water (the O in H2O)!
And as is so often the case in nature, these biological processes are cyclical. Unlike Humpty-Dumpty, water can be put back together again. Much of the very same water-derived oxygen that we breathe eventually is transformed back into water by our bodies. For example, with the help of O2, water is created when carbohydrates and fats are fully metabolized.
Even in the absence of life, water is full of activity, constantly rearranging itself. Its static formula, H2O, gives the impression that each and every water molecule is a stable entity; that once formed, in the absence of outside forces, these atoms are forever connected. This most definitely is not the case. Hydrogen atoms (H+) carrying a positive charge rapidly and constantly jump back and forth between adjacent water molecules. At room temperature, the H+ (proton) exchange rate between neighboring molecules is exceedingly fast, about 1000 times per second!
This proton-swapping process is a bit reminiscent of the game of musical chairs, played however at warp speed. Imagine the oxygens within every water molecule as the chairs. The protons then are like the players, standing up, moving about, and then sitting down on a different oxygen chair as the music starts and stops. The frequency of “atom trading” that occurs in 8 ounces of water—there are about 8 x 10^24 (that’s 8 followed by 24 zeros) molecules of water in 8 ounces—is astronomical, roughly 8 billion billion billion times every second.
Of course this is all happening on a scale way too small and far too fast for us to see; and in pure water, no net changes result. But this does not mean there are not important consequences to this extravagant behavior of water, even upon life itself. In a future article, I will examine just how vital this aspect of water is. The more fully we understand this amazing substance, the more deeply we can be thankful for a cold glass of water on a hot summer’s day. Water truly is the river of life.