All public water supply agencies heretofore or hereafter incorporated under the laws of the Commonwealth of Pennsylvania and holding a permit issued by the board under the provisions of this act, shall have the power and may exercise the right of eminent domain as respects the appropriation of the water and the water rights authorized by said permit and land covered by said waters: Provided, however, That such right shall not apply to private spring and private water supplies.
32 P.S. § 639