Lemonade gets a lift thanks to Thai basil, a variety of the herb that has a slightly spicy, licorice-ish flavor. Look for Thai basil at Asian markets or farmers’ markets. If you can’t find it, use regular basil.
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.