S.D. Codified Laws § 9-40-16
At or before the issuance of such revenue bonds the governing body by ordinance or resolution shall set aside, appropriate, and pledge the income and revenues of such utility, or such specified portion thereof as shall be determined by the governing body, into a separate and special fund or funds to be used and applied in payment of the cost thereof and in the maintenance, operation, repair, and depreciation thereof. Said ordinance or resolution shall provide that so much of the revenues from said utility as shall be necessary shall be set apart in a separate account and applied to the payment of the principal and interest of such revenue bonds and the accumulation of such reserve therefor as may be determined by the governing body to be necessary, and shall fix and determine as near as may be the monthly or annual proportion or amount of such income and revenues which is to be set aside as a proper and adequate depreciation account, and the balance shall be set aside and applied to the extent necessary for the reasonable and proper operation and maintenance thereof.
SDCL 9-40-16