As used in this article “county water district” means a county water district which has heretofore executed or shall hereafter execute a contract with the United States for any or all of the following purposes:
(a) Acquisition, extension, or operation of works for irrigation or drainage or flood control or the development of electric or other power.
(b) A water supply.
(c) Assumption as principal or guarantor of indebtedness to the United States.