In order to carry out the purposes and provisions of section 7 of Public Law 98-530, the district may establish, administer, and make a contribution in the amount of one million dollars to a separate fund, which shall consist of any monies received from the United States under section 7 of Public Law 98-530 and monies contributed to the fund by the district pursuant to this section. Monies from this fund are to be expended by the district at the direction of the board for the voluntary acquisition or conservation of water for use in central Arizona to supplement project water supplies in years when water supplies from the central Arizona project are insufficient to meet the water delivery schedules of non-Indian municipal and industrial users of project water supplies. Supplemental water acquired or conserved pursuant to this section shall be obtained exclusively from water users in this state holding decreed or contract rights to the waters of the mainstream of the Colorado river as of September 30, 1968.