conveyance to United States.] The title to all property acquired under the provisions of this act shall immediately and by operation of law vest in such irrigation district, in its corporate name, and shall be held by such district in trust for, and is hereby dedicated and set apart for the uses and purposes set forth in this act, and shall be exempt from all taxation; and said board is authorized and empowered to hold, use, acquire, manage, occupy and possess said property as herein provided; provided, that when any district contemplated in this act shall find it necessary to procure and acquire a supply of water from outside the boundaries of this state, then and in such event it shall be lawful for said district to contract and pay for the same in the same manner as other property acquired by the district is purchased and paid for: provided, further, that any property acquired by the district may be conveyed to the United States insofar as the same may be needed for the construction, operation and maintenance of works by the United States for the benefit of the district under any contract that may be entered into by the United States pursuant to this act.