Doctor N. J. McGee says: "Scarcely anywhere in the United States is the rainfall excessive, that is, greater than is needed by growing plants, living animals and men. Nearly everywhere it falls below this standard. In the western part the average rainfall is only about eighteen inches; in the extreme eastern part the fall averages forty-eight inches. In the western part much of the land is unable to produce crops at all except when artificially watered. The eastern part might produce more abundant crops, develop greater industries and support a larger population with a rainfall of sixty inches than it is able to do with a rainfall of forty-eight inches." As may readily be seen, the fly-off can be controlled only in a very small degree, by conserving the moisture that is in the soil, and so preventing it from evaporating too rapidly. The cut-off can be controlled to a considerable extent through forestry and scientific farming and it is very important that the supply should be as carefully conserved as possible. But it is in the run-off that the great waste of water occurs, and also that great saving is possible. It has been found by careful estimate that from eighty-five per cent. to ninety-five per cent. of the water that flows to the sea is wasted in freshets or destructive floods. We are not accustomed to think of the water as wasted, since it seems beyond our control, but as we are taking a careful account of stock, and seeing how our forests, our fuels and our minerals are disappearing, and our soil being carried out to sea by the rushing waters, it is well to consider, also, whether this great resource may not be so used as to benefit mankind in many ways and at the same time lessen the drain on other resources. The water of streams may be divided as to use into four great classes. The most important is that used by cities for general supply, for household and drinking purposes; next, that which is used for navigation and the running of boats to carry commerce; third, that which is used for artificial watering or irrigation, and lastly, that which is used for power in manufacturing. In the past, when water has been used it has seldom been employed for more than one of these purposes, but as we come to understand more the nature, value and possibilities of this great resource, we shall learn to make the money spent for one of these lines of activity supply several other needs. As we study each of these separately we shall see this interrelation among them.