It is even now practicable to develop water-power, wherever located, for the production of electricity. Although the lowest grade coals are used for electric power at the mines yet they can now be used for still other purposes. Coal or other fuel once used can not be replaced, but when electricity is derived from water-power only energy otherwise wasted is used. This energy, if derived from water-power, is all added to our assets instead of being lost. For many years the amount of power used for manufacturing and other purposes has doubled about once in ten years, and the steady pace kept by different lines of development shows how closely they are related. Our power, our forest cut, the use of our iron and other minerals, our coal and petroleum, the railroad earnings, freight and passenger traffic, and our agricultural products all double themselves every ten years. This means that in ten years we shall require twice as much power as now, but will have far less coal to use. This raises the question,--have we available water-power to conserve our coal supply? Let us see. It is estimated that we are now using 26,000,000 horse-power of energy derived from steam, 3,000,000 horse-power derived from water, and 800,000 from gas or oil, a total of 29,800,000 horse-power. It is also estimated that there is now running idly over dams, falls, and rapids 30,000,000 horse-power of energy. In other words, we are wasting every day enough water to run every factory and mill, and to turn every wheel, to move every electric car and to supply every electric light or power-station in the country. The amount of water-power is gauged solely by the low-water stage of the stream. A river is considered to produce only as much power as it can furnish at its season of lowest water. At other times factories may be operated more actively, but usually most of the extra power is wasted during a large part of the year. If these storm or flood waters can be stored in reservoirs, the stream-flow throughout the year can be made fairly uniform and the power possibilities greatly increased. The Geological Survey believes that by storing the flood waters and regulating the flow of the streams, the large rivers of the United States may be made to furnish 150,000,000 horse-power, enough, if it could be utilized, to supply every power need of our country for many years to come without using a ton of our coal, and without in any way decreasing the water.