S.D. Codified Laws § 46A-3B-13
For any water development district with boundaries affected by §§ 46A-3A-2 to 46A-3A-5, inclusive, any director of the district who is in office on January 1, 2009 shall continue to serve as a director if the director remains a resident of the district. At the first general election after January 1, 2009, for any water development district with boundaries affected by §§ 46A-3A-2 to 46A-3A-5, inclusive, directors shall be elected for all director positions in the district, regardless of whether or not any director's term has expired. The directors elected for the district at the general election shall be elected to serve for staggered terms. Thereafter, directors shall be elected to four-year terms at each subsequent general election to succeed those directors whose terms expire at the end of the year in which the election is held.
SDCL 46A-3B-13