No levy of an ad valorem tax under ORS § 553.710 for any one year shall exceed one-half of one percent (0.005) of the real market value of all taxable property within the subdistrict, computed in accordance with ORS § 308.207. If the total sum of money required to be raised under the terms of a contract entered into by a district, together with the sum of money to be raised to pay the costs and expenses of the district incurred in connection therewith, exceeds such limitation, a levy for each year thereafter shall be made by the district until the entire contract obligation has been discharged. [Amended by 1963 c.9 § 31; 1991 c.459 § 432]