ring water and ginger to a boil in a large sauce pan. Pour water over tea bags in a teapot or 4-cup heat-proof measuring cup; steep 3 minutes . Remove and discard tea bags. and ginger. Stir in 1/4 cup sugar; cool tea to room temperature.
Mix remaining 1/4 cup sugar with lime juice ; add to tea. Pour tea into 4 ice-filled glasses. Garnish with lime slices.