Idaho Code § 42-2802
The board of county commissioners may enlarge, improve or extend existing reservoirs, canals and other irrigation and drainage works to provide for the irrigation or drainage of additional lands in such county, or to improve the water supply or drainage for such lands, and may contract with the owners of existing irrigation or drainage works to provide for such enlargement, improvement or extensions, and may purchase and complete incomplete irrigation or drainage works and may purchase assignments of partially paid reservoir or storage rights and the assignment of such contracts, and may complete payment thereon and acquire such storage and reservoir rights for the reclamation or more complete irrigation of lands in such county, and in so doing shall proceed in similar manner as in the case of entirely new works but subject to the same condition as to approval of the bond issue by the electors of the county.
Idaho Code § 42-2802