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~eficlency for thdltower Basin lll(a) and 1It(b) apportionments mll.st be equal to the deficiency for the Upper Basin's III (a) 2ppor- tionment before demand can be made on the states of the Upper Division for water for Mexico. It has been argued by some that reservoir evaporation is not accountable as beneficial use under the 1922 Compact.' This argument does not appear well founded, but in the unlikely event that it would prevail the total amount of water accountable as available for beneficial consumptive uses in the two basins and for~elivery to Mexico would be reduced by 1.2 maf annually . . _to account for reservoir evaporation in the Lower Basin and about 0.5 maf an~ually to account for reservoir evaporation in the Upper Basin. However, if a conservative estimate of 10 maf annually available in the Lower Basin is adopted, the Upper Basin would still be able to deplete 6.5 maf of an average annual Lee Ferry flow of 14 maf; but only about 6.0 maf of this depletion woulu be chargeable as beneficial consumptive use. It has also been argued that uses from Lower Basin tri- butaries are not accountable in determining the Lower Basin's beneficial consumptive use and Treaty obligation. This argument, and the argument concerning the accountability of reservoir evaporation as beneficial consumptive use may arise out of a misunderstanding of the 1963 Supreme Court decision in Arizona vs. California, et a1. It is important to remember that the Court in that case interpreted the Boulder Canyon Project Act and found it unnecessary to interpret the Compact. Thus it \vas unnecessary for the Court to rule on the question of whether reservoir evaporation and tributary uses are accountable as beneficial consumptive use under the Compact. The apportiOJnents -11-