Idaho Code § 43-118
Where the petition or petitions for the organization of any irrigation district now or hereafter organized under the laws of the state of Idaho, includes lands lying under any existing irrigation canal or canals, and entitled to receive water therefrom for irrigation purposes, and such petition or petitions recite that it is proposed to construct or purchase or acquire an interest in any reservoir, or reservoirs constructed, or to be constructed by or in cooperation with the United States or under contract with the United States, the decree of the district court confirming the organization of such irrigation district shall recite such provision of said petition, or petitions, and the landowners of said district who by reason of stock ownership (in the canal company or companies owning or operating any of such existing canal), or otherwise, own or are entitled to the use of canal capacity or a proportionate interest in any such canal, shall be entitled to have delivered into such canal for the use and benefit of such landowners their proportionate share of the district's share of the stored water from such reservoir in the proportion that their lands are assessed for such reservoir, in such amounts, or at such rate of delivery as may be needed by the landowners not in excess of the amount which can be safely carried through such landowners' proportionate share of such canal, whenever such canal is not being utilized to its full capacity in carrying the natural flow or other water owned or controlled by the canal company operating said canal and the board of directors of such district shall have power to provide by contract for the carriage and distribution of the stored water from such reservoir to the landowners of the district through such existing canals, but such district shall be without power to purchase or condemn or otherwise acquire, or to operate or control any such canal, unless such petition for the organization of such district shall also recite the purpose to acquire such canal or canals.
Idaho Code § 43-118