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Show CLASSIFICATION OF AVAILABLE WATER SUPPLIES 23 Underflow of surface stream is the subsurface portion of a watercourse the whole of which comprises waters flowing in close association both on and beneath the surface. Percolating water is water moving through the ground but not constituting part of a definite underground stream. Artesian water is ground water under sufficient hydrostatic pressure to rise above the saturated zone. An available supply of water differs from that of certain other natural resources-such, for example, as deposits of iron ore or precious metals, or even oil-in that it is in a state of continuous or intermittent replenishment from other sources of water supply, through the cyclical operation of physical laws. Thus, in the western United States, watercourses and diffused surface waters are supplied chiefly by precipitation in storms originating over the Pacific Ocean and the Gulf of Mexico; diffused surface waters sink into the ground or become concentrated in stream channels, thereby augmenting the supply of ground water or of surface streams; surface streams feed subterranean supplies at some places and are fed from subterranean sources at others, and disappear into the ground or flow into the sea or into lakes either with or without known surface outlets; and water evaporates from all surface supplies and from subterranean supplies close to the surface and is deposited in the form of precipitation elsewhere. A water supply, therefore, is almost never in truly static condition, awaiting exploitation by man. Its particles are generally in motion-they have come from some other water supply or supplies, and are en route to still others. Therefore, diversion of water from a particular source of supply interrupts the natural replenishment of some other available source of supply. Recognition of this fundamental relationship is necessary to an orderly discussion of water rights.^ The point at which water is physically appropriated for use-that is, diverted from its natural state and brought under control by artificial devices- determines the initial legal classification of such water for such use. Thus, waters taken from a stream into a canal, through a headgate installed on the bank of the stream, are classified at the point of diversion as waters of a watercourse. Waters diffused over the ground and which if not intercepted would flow over a bank into a stream, but which before doing so are captured by means of an artificial dike and thereby simply detained or directed into a canal, are classified at the point of interception as diffused surface waters. Waters moving through the soil, which if not intercepted would seep into a surface watercourse through the banks or bottom of the channel, but which are captured and brought to the surface by means of a pumping plant installed some distance away from the stream and its subterranean channel, are classified at the point of interception as percolating waters or as waters of definite underground streams, depending upon the geological structure through which they are moving. However, a watercourse flow, or a ground water reservoir, |