Bring 6 cups water and hibiscus flowers to a boil in a large saucepan. Reduce heat to low, and simmer 5 minutes. Remove from heat, and stir in sugar.
Pour mixture through a wire-mesh strainer into a pitcher, discarding hibiscus flowers. Stir in remaining 1 cup water. Serve over ice.
*6 regular-size Red Zinger tea bags may be substituted for 1 cup hibiscus flowers.
Note: Hibiscus flowers may be found in Mexican or Latin supermarkets.