Wat. Code, § 23198

When a contract has been made with the United States, if so provided by the contract and authorized pursuant to this chapter, bonds of the district may be transferred to or deposited with the United States, at not less than 95 percent of their par value, to the amount or any part thereof to be paid by the district to the United States. The interest or principal or both on the bonds shall be raised by assessment and levy as prescribed in this chapter and shall be regularly paid to the United States and applied as provided in the contract. The bonds may provide for the payment of interest at a rate not exceeding 8 percent per year, be of the denominations, and call for the repayment of the principal at the times, all as agreed upon.