Thai Basil Lemonade

In a large bowl, using a muddler or the handle on a wooden spoon, smash the sugar, basil, and lemon halves until very fragrant, 2 to 3 minutes. Add 8 cups water and the lemon juice. Stir until the sugar dissolves. Cover and refrigerate until the flavors meld, about 2 hours. Strain into a pitcher. Add ice to the pitcher just before serving.