Neb. Rev. Stat. § 46-1,143

The board of directors of any irrigation district organized under the laws of this state may enter into contracts for a supply of water for the irrigation of the lands within such irrigation district with any person, firm, association, corporation or the United States of America. The source of supply of such water may be either within or without the boundaries of the State of Nebraska, and the water supply may be either the entire supply of water for such district or to supplement an appropriation already made by such district.