Boulder City Act Amendments of 1979 - Amends the Boulder City Act of 1958 to authorize the Secretary of the Interior to transfer to Boulder City, Nevada, portions of the Federal interest in the water supply system if such municipality agrees to reimburse the United States for the operating and maintenance costs of the water delivery system. Repeals: (1) the ceiling on the costs of supplying water; (2) the provisions concerning the costs of operating such system; (3) the requirement that the Secretary determine the number of employees on such project; and (4) the requirement that the Secretary report to Congress every five years concerning the need for assistance to such municipality.