The best results of this system are undoubtedly achieved by the use of iron pipes for the distribution in field and orchard, whatever may be the material used for the main conduits. The use of concrete and tile in small sizes proves in the end very expensive, because of frequent breakage, and leakage due to varying pressure in the supply pipes or reservoirs; as well as from even slight earthquake tremors, undermining by water or by the burrowing of animals, and many other accidents which do not affect an iron pipe system. The pipes must in any case, of course, be laid deep enough to be out of reach of the deepest tillage; therefore not less than one foot, and preferably eighteen inches. A proper construction of the outlets, permitting of exact regulation of the flow and ready operation from above ground, as well as preventing their being clogged by earth, rust, roots or burrowing animals, insects etc., is of course of the greatest importance. A variety of devices for this purpose is already on the market. QUALITY OF THE IRRIGATION WATER. _Saline Waters._—Considering the large amount of water annually used in irrigation, among the most needful precautions to be observed by the irrigator is in the testing of the quality of his water-supply. First among the points to be noted is the possible content of soluble “alkali” salts. While in most cases what is called the “rise of the alkali” is due to the salts already contained in the soil and subsoil, in but too many the evil is either brought about, or greatly aggravated, by the excessive saline contents of the water used in irrigation. The effects of the use of saline irrigation water (containing in this case about 100 grains per gallon, or 1700 parts per million) are shown in the accompanying plate. The predominant ingredients of these alkali salts were common salt and carbonate of soda. In the lands near Corona, Cal., where this case was observed, the original alkali-content of the soil was about 2500 pounds per acre in four feet depth, and had been just quadrupled, with the results shown; viz., complete defoliation of the orange trees, while on the same land, where the trees had been irrigated with good artesian water, the orchard was in fine condition. _Limits of Salinity._—It is not easy to assign a definite limit of mineral content beyond which water should be considered unfit for irrigation purposes; partly because of the differences in the kind of the mineral salts, partly because the nature of the soil and the amount of water at command, materially influence its availability. [Illustration: FIG. 44.—Orange Trees Irrigated with Artesian Water.] [Illustration: FIG. 45.—Lake Elsinore Water, Three Years.]