All municipalities, public bodies and public agencies operating water district systems in and adjacent to Edgefield County shall be fully empowered to enter into contracts to buy water from the Authority. Such contracts shall extend over such period of time and shall contain such terms and conditions as shall be mutually agreeable to the Authority, and to the contracting municipality, public body or public agency. No municipality or other agency operating water systems shall extend its present facilities beyond the corporate limits without prior written approval of the Authority.