Idaho Code § 42-2981
Lands, whether public or private, which have been developed for commercial, industrial, recreational, residential, governmental or highway purposes, and from which surface water or seepage drain into the irrigation or drainage system of any person or persons, canal company, irrigation district, drainage district, or ditch owners' association, shall be liable for a proportionate share of the cost and expense of operating, maintaining, repairing and replacing the portions of such system which are used or allocated for drainage purposes. Drainage charges for any such lands which are not subject to the regular assessment powers of the person or entity owning or controlling the system shall be billed to, and shall be paid promptly by, the governmental unit owning the land. If the lands are privately owned, the drainage charges shall be billed to, and shall be paid promptly by the county in which the lands are located, and such charges shall be included in the county budget as a separate fund for drainage, the tax for which shall be levied against all privately owned lands in the county which are benefited by such drainage and which are not subject to the regular assessment powers of the owner of the irrigation or drainage system.
Idaho Code § 42-2981