A district may, at any time after entering into a contract for a project to be financed in whole or in part by special assessments, issue temporary and definitive warrants on the project fund, created for that purpose, in the manner and subject to the limitations prescribed in section 40-24-19. If the warrants are issued to finance a sewer or water project, the net revenues derived from the imposition of service charges to be imposed and collected with respect thereto as provided in section 40-22-16 may be pledged to payment of those warrants, except that the first maturity date of any such warrant shall not be less than two years from the date of issuance. Warrants issued under this section shall be in such amounts as in the judgment of the water resource board will be necessary for the project. The warrants shall bear interest at a rate or rates and be sold at a price resulting in an average net interest cost not exceeding twelve percent per annum if sold at private sale. There is no interest rate ceiling on warrant issues sold at public sale or to the state of North Dakota or any of its agencies or instrumentalities. Coupons evidencing the interest for each year or half year, as the case may be, may be attached to the warrants. The warrants shall state upon their face the purpose for which they are issued and the project fund from which they are payable and shall be signed by the chairman of the water resource board and countersigned by the secretary of the district. The warrants shall be payable serially in such amounts as the board determines, extending over a period of not more than thirty years.