S.D. Codified Laws § 46A-9-17
All water user districts, created under the provisions of this chapter, and additions to and deletions from the districts, established or purporting to be established or adjusted before July 1, 1978, pursuant to the provisions of this chapter and having a de facto existence of at least one year, are hereby declared to be valid and legally created political subdivisions of the state. The regularity and validity of the creation of such water user districts in existence for one year or any boundary adjustments of the districts is not open to question in any court in the state. All acts and proceedings of any water user district or of its board of directors, or both, leading up to the authorization and execution of an existing contract between any water user district and the United States of America, and all acts and proceedings of any water user district or of its board of directors, or both, leading up to the issuance and deliverance of bonds of any water user district are hereby legalized, ratified, confirmed, and declared valid to all intents and purposes. All existing contracts and outstanding bonds are hereby legalized and declared to be valid and legal obligations of and against the water user district executing or causing the execution of the contracts or bonds. This section does not apply to any suit or proceeding legally initiated before July 1, 1978.
SDCL 46A-9-17