S.D. Codified Laws § 46A-9-66
The board of directors shall provide in the proceedings authorizing the issuance of each series of bonds, warrants, notes, debentures, or other evidences of indebtedness or in the trust indenture securing the same, for paying into the appropriate debt service fund at stated intervals all moneys then remaining in the water fund, after paying all costs of operation, maintenance, and repairs of the works and all administrative and clerical expenses of the water user district. All moneys in each debt service fund shall be pledged for the payment of and used for the purpose of paying the interest, principal, and the necessary fiscal agency charges upon the bonds, warrants, notes, debentures, or other evidences of indebtedness as the same shall fall due.
SDCL 46A-9-66