In case the district has its works partially completed and bonds authorized and outstanding, the proceeds of which have been used for the construction of said works, the said district may enter into a contract with the United States for the completion of the works of the district, and shall have power to transfer title to the works already completed, or any portion thereof, to the government, and shall have power to redeem its outstanding bonds on any such terms as may be agreed upon, with funds advanced by the United States, and contract with the United States to repay any such funds, as well as additional cost of construction for the completion of the works, on such terms as may be agreed upon by contract between the district and the United States: provided, that no contract with the United States embodying any of the provisions herein contained shall be binding unless ratified by two-thirds (2/3) of the voters voting at an election to be held for that purpose in the manner provided for the ratification of a bond issue: except, that the board of directors of an irrigation district, on behalf of the district, may make a temporary contract with the United States for a period of not to exceed one (1) year for the purpose of securing a water supply for the district out of the reservoirs or other irrigation works of the United States during said period, or a portion thereof, or providing for the distribution and delivery thereof and may provide for the payment therefor and pay for the same by means of a toll charge or by means of an assessment as a part of the annual operation and maintenance cost of the district.