Any irrigation district organized under the laws of this state may accept the provisions of any act of the Congress of the United States applicable to such district and may obligate itself to comply with such laws, rules, and regulations as may be promulgated by any department of the United States in pursuance of such acts. An irrigation district contracting with the United States under the provisions of this chapter shall be governed in all matters by the laws of this state    relating to irrigation or drainage districts, as the case may be, except in such things as may be provided otherwise, for such district. The provisions of this section shall not limit the rights which any irrigation district has under existing laws to purchase a water supply or otherwise to contract and shall be cumulative thereto.