1. Make simple syrup: Combine sugar and 2 cups water in a saucepan over medium heat. Bring to a boil and stir until sugar has dissolved. Remove from heat and cool to room temperature.
2. Pour lemon juice into a large pitcher. Add simple syrup and stir to combine. Refrigerate until cold.
3. When ready to serve, add 6 cups of cold water and stir. Taste, and add more water if it's too sweet.
4. Serve with ice, thinly sliced lemons and fresh mint, if desired.