Idaho Code § 42-1402
In allotting the waters of any water system by the district court according to the rights and priorities of those using such waters, such allotment shall be made to the use to which such water is beneficially applied, except where water rights established under federal law are involved, in which case the allotment shall be made in accordance with federal law. The right confirmed by such decree or allotment shall be appurtenant to and shall become a part of the land on which the water is used, and such right will pass with the conveyance of such land, and such decree shall describe the land to which such water shall become so appurtenant. The amount of water so allotted shall never be in excess of the amount actually used for beneficial purposes for which such right is claimed, or in the case of a water right established under federal law, in excess of that amount determined by federal law.
Idaho Code § 42-1402