Such operation and maintenance assessment shall be apportioned pursuant to the provisions of section 5 of the Act of Congress of August 13, 1914, known as the reclamation extension act, upon the basis of the number of acre-feet of water delivered during the preceding irrigation season but with a minimum charge upon each acre of irrigable land whether irrigated or not for delivery of not less than one (1) acre-foot of water.
Idaho Code § 43-1824