S.D. Codified Laws § 34A-3-4

All water treatment plants, wastewater treatment plants, water distribution and wastewater collection systems, serving a demand equal to five hundred or more persons and all water treatment plants using surface water or groundwater under the direct influence of surface water, in whole or in part, whether publicly or privately owned, shall be under the supervision of an operator whose competency is certified to by the secretary in a grade corresponding to the classification of that portion of the system to be supervised. Beginning January 1, 1993, all water treatment systems utilizing disinfection equipment shall be under the supervision of a certified operator.