A deluge of counties and cities on Monday joined in the war for water among Georgia and Florida that centers on Lake Lanier and the Chattahoochee River basin. Gainesville joined with the Atlanta Regional Commission, Forsyth, Gwinnett, DeKalb and Fulton counties and the Cobb County-Marietta Water Authority in filing an amicus brief on Monday with the U.S. Supreme Court. It argues that Florida had not proved that tighter water-use restrictions on Georgians would benefit Florida residents.