S.D. Codified Laws § 46A-9-8
In the petition, if directors are to be elected at large, the directors named shall be divided as nearly as possible into three equal groups, to be designated Group 1, Group 2, and Group 3, respectively. In either case, the members of Group 1 shall hold office until their successors, elected at the first regular water user district election thereafter, shall have qualified; the members of Group 2 shall hold office until their successors, elected at the second regular district election thereafter, shall have qualified; and the members of Group 3 shall hold office until their successors, elected at the third regular district election thereafter, shall have qualified. Thereafter all directors elected shall serve for a term of three years and until their successors are elected and qualified. After the name of each director shall be stated to which of said three groups he belongs.
SDCL 46A-9-8