S.D. Codified Laws § 46-1-4
It is hereby declared that, because of conditions prevailing in this state, the general welfare requires that the water resources of the state be put to beneficial use to the fullest extent of which they are capable, and that the waste or unreasonable method of use of water be prevented, and that the conservation of such water is to be exercised with a view to the reasonable and beneficial use of the water in the interest of the people and for the public welfare. The right to water or to the use or flow of water in or from any natural stream or watercourse in this state is limited to an amount of water reasonably required for the beneficial use to be served, and such right does not extend to the waste or unreasonable use or unreasonable method of diversion of water.
SDCL 46-1-4