When a water resource board, by resolution, has caused special assessments to be levied to cover the cost of constructing a project, the board shall determine the rate of interest unpaid special assessments must bear. The interest rate may not exceed one and one-half percent above the warrant rate. Interest on unpaid special assessments must commence on the date the assessments are confirmed finally by the board. Special assessments may be certified and made payable in equal annual installments, the last of which must be due and payable not more than thirty years after the date of the warrants to be paid. The secretary of the district shall certify to the county auditor of the county in which the district is situated, or if the district embraces more than one county, to the county auditor of each county in which district lands subject to the special assessments are situated, the total amount assessed against lands in that county and the proportion or percentage of the amount assessed against each piece, parcel, lot, or tract of land. The secretary of the district also shall file with the county auditor of each county in which district lands lie a statement showing the cost of the project, the part of the cost, if any, to be paid out of the general taxes, and the part to be financed by special assessments. Funds needed to pay the cost of maintaining a project may be raised in the same manner as funds were raised to meet construction costs. If the project was financed in whole or in part through the use of special assessments, the water resource board shall prorate the costs of maintaining the project in the same proportion as the original costs of construction or, in the event a reassessment of benefits has been adopted, the board shall prorate costs in accordance with the reassessment of benefits.