S.D. Codified Laws § 34A-5-38
If bonds are issued in lieu of special assessment certificates in accordance with the provisions of chapter 9-43, the sanitary district board of trustees may provide that rates and charges shall be fixed and from time to time revised to produce net revenues at all times sufficient, with special assessments and interest pledged to the bond fund and actually collected and received in the bond fund, to pay all principal and interest when due on the bonds and to create and maintain such further reserves for the security of the bonds as may be agreed in the resolutions authorizing the bonds. Bonds issued and secured as authorized in this section may be designated as special assessment and revenue bonds, and may be issued to finance an improvement or a group of improvements to the facilities of the district, if any portion of the cost of the improvement is to be paid by the levy of special assessments.
SDCL 34A-5-38