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29 ,Oil22G9 Desalting Alternative Plan To supply 1,200,000 acre-feet annually for the projected municipal and industrial water demands in Central Arizona, a desalting plant complex would be created in the Yuma area drawing upon the Gulf of California for its basic sea-water supply. Cooperation with Mexico would be essential to this alternative. . The complex built by stages with ultimate annual deliveries of 1,200,000 acre-feet would cost about $900,000,000 for desalting plants and connecting ocean intake and return channels but exclu- sive of associated thermo-electric generating plants. Desalted water made available at Imperial Dam would be exchanged, to the users diverting through the Imperial Dam head works, for Colorado River waters at Lake Havasu. From Lake Havasu an aqueduct system parallel to the Granite Reef Aqueduct would be constructed to central Arizona. This parallel aqueduct system would cost about $353,000,000. This same capacity if built initially into the Granite Reef Aqueduct would add about $190,000,000 to the Phase I construction for an overall saving. An alternative aqueduct from Imperial Dam to the Phoenix and Tucson metropolitan areas would cost about $400,000,000 to take the high quality water directly to the municipal and industrial use area. The estimated annual operating costs for this alternative supply would be $78,400,000 for the desalting plants and $9,630,000 for the parallel aqueduct system. The type of desalting plants considered in this alternative are summarized below and further described in the Appendix of the Office of Saline Water. . The flash-type distillation process has been most extensively studied, with design concepts for very large plants--up to 150 mil- lion gallons per day. The current state of development limits the size of plants utilizing other processes to about 5 - 10-million- gallon-per-day size. These processes may be effectively utilized to supply high quality water to meet municipal demands of smaller cities that cannot be economically served by conveyance facilities. Results show that the flash distillation process maximizes the use of equipment items that have been previously developed in large sizes for other purposes, and can also be readily adapted to use steam from a topping turbine, resulting in a cheaper source of steam. A combination steam-electric and water plant using the flash distillation process has been investigated using both coal and gas as a fuel source. Based on present technology a unit of 150-million- gallon-per-day fresh water capacity, constructed in combination with