In small saucepan, over medium heat, combine sugar with 1 cup water; stir until sugar is dissolved. Add rosemary and mint; crush with wooden spoon to release flavors. Bring mixture to a boil; reduce heat and simmer 5 minutes. Set aside about 5 minutes to cool slightly.
Pour herb mixture through fine strainer into pitcher. Stir in lemon juice and 3 cups cold water.