20

THE USE OF WATER

The "duty of water" is the term used to express the relation between the quantity of water used in irrigation and the area upon which it is employed. The present duty of water in Texas can not be ascertained with the data in hand, but is in most cases very low. The duty assumed by most of the projectors of new irrigating enterprises is 100 acres to the second-foot. This, in the semiarid section at least, ought to prove sufficient, for by the time the amount of land under irrigation from each canal reaches the maximum the people will have learned how to use the water more economically than at first, and the land will not require so much. A careful estimate of the amount of land under irrigation in Mexico, just across the international border at Eagle Pass, gives a duty of 137 acres to the second-foot. There the crops are mainly corn and cotton, the latter needing very little water.

The investigations upon which this discussion is based revealed the fact that there are in the State not only a great variety of gravity systems of supplying water but also all kinds of pumping devices operated by steam or gasoline engines and by water wheels or windmills. The latter are of more importance than the data obtained would seem to indicate. Throughout the arid and semiarid regions nearly every residence has its windmill to pump water for domestic uses, the surplus of which is often used to irrigate a few vegetables or fruits around the house. Although a small area is watered by each mill, yet the aggregate must be considerable. Data were obtained from the few plants constructed for irrigation use only, which will give an idea of the comparative merits of windmills as a source of irrigation. The least cost of a windmill-irrigation plant was found to be a little over $16 for each acre irrigated, the largest area watered by one wheel being 30 acres. This is in the humid portion of the State. In the arid portion half that amount is all that can be supplied. The average cost is about $47 for each acre irrigated, and the area commanded by each wheel amounts to only about 7 acres. The number of acres irrigated from each steam or pumping plant varies from 5 to 1,000. The cost of these irrigation plants ranges from $15 to $50 for each acre irrigated. The efficiency of most of the pumping plants could and should be very largely increased. There is a great lack of experience shown in the management of many of them, and consequently they have not been operated at anything like their full capacity or made to pay a reasonable dividend on the money invested. Few of them have reservoirs into which to pump the water; thus they can be used only while the actual irrigation is going on, whereas to be operated economically they should be run day and night, at least during the irrigating season. There are