In addition to the purposes otherwise authorized by law, irrigation districts may be organized for the purpose of cooperating with, and all irrigation districts organized under this chapter shall have the power to cooperate and contract with, the United States under the reclamation laws of the United States for the purpose of constructing irrigation or drainage works or levees for the protection of lands in the district, or for acquiring, purchasing, extending, operating or maintaining works already constructed, or supplying water, or for assuming indebtedness of the United States, as principal or guarantor, on account of or affecting lands of the district.