Idaho Code § 42-913
Any person or persons owning or controlling land which has or has not been irrigated from any such canal, shall on or before January first of any year, inform the owner or person in control of such canal whether or not he desires the water from said canal for the irrigation of land during the succeeding season, stating also the quantity of water needed. In distributing water from any such canal, ditch or conduit during any season, preference shall be given to those applications for water for land irrigated from said canal the preceding season, and a surplus of water, if any there be, shall be distributed to the lands in the numerical order of the applications for it. But no demand for the purchase of a so called perpetual water right, or any contract fixing the annual charges or the quantity of water to be used per acre, shall be imposed as a condition precedent to the delivery of water annually as provided in this chapter; but the consumer of water shall be the judge of the amount and the duty of the water required for the irrigation of his land; and the annual charges to be made and to be fixed under the further provisions of this title, shall hereafter be based upon the quantity of water delivered to consumers, and shall not in any case depend upon the number of acres irrigated by means of such amount of water delivered.
Idaho Code § 42-913