Iowa Code § 468.157: Payment.

All compensation for services rendered, fees, costs, and expenses when properly shown by itemized and verified statement shall be filed with the auditor and allowed by the board in such amounts as shall be just and true, and when so allowed shall be paid on order of the board from the levee or drainage funds of the district for which such services were rendered or expenses incurred, by warrants drawn on the treasurer by the auditor.