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2 Ou227S THE WATER-SUPPLY SITUATIOIT DT BRIEF With facilities in existence and under construction, regulation of the main-stem Colorado River in the Pacific Southwest soon will be close to the optimum. To the west, in southern California, streams have lIIlIIIJ.l. perennial flows or are intermittent; they have been developed about to the maximum. Ground-water bodies are drafted heav11;y in the areas of greatest population density; locally, especially in central Arizona, they are being overdrawn currently. . In the aggregate, use of water within the region now approaches the perennial capacity of local sources. With increasing population, total requirement of water will surpass that perennial local capacity'. Further, domestic and industrial uses take a steadi1;y increasing percentage of total water supply. Agricultural use, principal1;y for irrigation, doubtless will continue to diminish as a percentage of the total; it may diminish as a volume. Thus, the pattern of water require- ments within the region is not stable as to either place of use or seasonal d:l.stribution of use. Under the, recent decision of the Supreme Court of the United States, in Arizona v. California, more main-stem water of the Colorado River prospectively will be used in central Arizona and less will be used in southern California. This geographic shif't in use aggravates the unstable use pattern just noted. Eventually, this prospective shift of Colorado River water to Arizona 101111 be compensated under the California Water Plan, which will convey surplus water of the nortb to the water-deficient south, within the State. However, such compensa- tion cannot be accomplished quickly. For its economic integrity, the region must wring maximum productivity from all local water sources. A comprehensive region-wide plan to that end is essential. Alternative sources--such as desalted ocean water in the coastal area or imports from remote streams--would be substantially more costly and would not be justified who1ly by the . truism that the day of low-cost water is gone. Beyond optinnnn regulation of the Colorado River main stem, which is imminent, ,all sources of water within the region, surface and under- ground, must be managed jointly for optimum perennial yield. The cost of developing water supplies undoubtedly will rise and will force IOOre intensive use and re-use of water. probably IOOst critical, means must be devised for effective management and disposal of wastes--llIllI11cipal, industrial, and agricultural--so that current and prospective depre- ciation of water quality can be held to the practical minimum. ibe need for resolving these and related matters in the Pacific Southwest is urgent. Equal urgency in other regions of the nation may well be at lesst a generation in the future.