Water Contained in our Food is Pure. Seeing that five-sixths of our food is water, it is clearly of the greatest importance that that water should be pure. That part of our water supply which we get in and with our foods is fortunately, for the most part, almost perfectly pure, having been specially filtered by the plants or animals which originally drank it, or having been boiled in the process of cooking. [Illustration: THE SPOUTING FOUNTAIN Where no lips need touch the cup.] Water is Always in Motion. The part of our water supply which we take directly, in the form of drinking water, is, however, unfortunately anything but free from danger of impurities. The greatest difficulty with water is that it will not "stay put"--it is continually on the move. The same perpetual circulation, with change of form, but without loss of substance, which is taking place in the engine and in our bodies, is taking place in the world around us. The water from the ocean, the lakes, and the rivers is continually evaporating under the heat of the sun and rising in the form of vapor, or invisible steam, into the air. There it becomes cooler, and forms the clouds; and when these are cooled a little more, the vapor changes into drops of water and pours down as rain, or, if the droplets freeze, as snow or hail. The rain falls upon the leaves of the trees and the spears of the grass, or the thirsty plowed ground, soaks down into the soil and "seeps" or drains gradually into the streams and rivers, and down these into the lakes and oceans, to be again pumped up by the sun. All we can do is to catch what we need of it, "on the run," somewhere in the earthy part of its circuit. Why our Drinking Water is Likely to be Impure. Every drop of water that we drink or use, fell somewhere on the surface of the earth, in the form of rain or snow; and if we wish to find out whether it is pure and safe, we must trace its course through the soil, or the streams, from the point where it fell. Our drinking water has literally washed "all outdoors" before it reaches us, and what it may have picked up in that washing makes the possibilities of its danger. As it falls from the skies, it is perfectly pure--except in large cities or manufacturing centres, where rain water contains small amounts of soot, smoke-acids, and dust, but even these are in such small amounts as to be practically harmless. But the moment it reaches the ground, it begins to soak up something out of everything that it touches; and here our dangers begin.