HOW COME?: We humans are mostly all wet

Even far away from the ocean, we're surrounded by water. Water hides in the air we breathe, becoming visible in clouds and fog. And then there are the very watery leaves, grass and flowers of the spring day outside. Oh, and that apple you ate for lunch, which seemed so solid and crunchy? About 84 percent water. And don't forget the (rather spongy) brain you're using to read this -- a whopping 78 percent water.

As for the rest of the body, the answer is: It depends. It turns out that some of us are more watery than others. Newborn babies are about 75 percent water by weight. But the percentage drops as we grow, and the average adult body is about 57 percent water. Surprisingly, the more body fat we carry, the lower the percentage. An obese body may be only about 45 percent water.

Water is known as the universal solvent, because so many things will dissolve in it. Like oxygen in our watery blood.

How does it work? Water molecules act as such powerful dissolvers because of their shape. Water -- or H2O, -- is made of two atoms of hydrogen and one of oxygen Linked together, the three atoms form a triangle.

Each triangle is positively charged at the bottom, where the two hydrogen atoms angle away from each other, and negative at the top, where the oxygen atom perches. So each water molecule has a kind of electrical polarity (rather like the polarity of a magnet, with its own opposite ends).

When certain substances -- say, salt -- are plunked into water, their molecules are pulled apart by their electrical attraction for the water molecules. Presto: a disappearing act, a seamless blending that saves us from soup with a mound of salt at the bottom of the bowl.

Our bodies run on water. Every organ, from brain to heart to liver, is a water-filled mass, fed by red, watery blood carrying dissolved sugar (glucose), minerals, gases (like oxygen and carbon dioxide) and hormones. Thanks to water's solvent properties, waste filtered through our kidneys can be dissolved and safely carried away.

To keep us from overheating, water seeps through pores as sweat, evaporating into the air. Our gas-exchanging lungs must stay damp in order to work. Our eyes are continuously moistened by a watery film. Like a hinge that needs oil, our knee and elbow and hip joints require water to move our legs and arms. Our skin must be plumped by water or it will dry out and crack, inviting infection. And our muscles, including our beating hearts, are 77 percent water.

Since we are always losing water through sweat, breathing, urine and feces, we must constantly replenish our supply, through eating and drinking. With no access to water in any form, a human being can only survive about three to six days.