S.D. Codified Laws § 9-26-27
All taxes so levied when collected shall be placed in a special debt service fund and no part thereof shall be used for any purpose other than to pay the interest and principal of the bonds for which they were levied and collected; provided, that if any moneys shall upon the expiration of any fiscal year be transferred from other funds and irrevocably appropriated to said debt service fund, pursuant to the provisions of § 9-21-26.1, the governing body may in its discretion cause the amount so transferred to be certified to the county auditor, who shall thereupon reduce the levy to be spread upon the tax lists for collection in the following year by the amount so certified, or by such lesser amount as shall be directed by the governing body.
SDCL 9-26-27