Using a vegetable peeler, zest 1 lemon in strips; juice the zested lemon and remaining lemons into a measuring cup. in a saucepan, bring 1 cup basil, 3/4 cup water, the zest and sugar to a boil over medium-high heat, stirring until the sugar dissolves, about 3 minutes. remove from the heat and let steep 10 minutes. Strain the basil syrup through a fine sieve. refrigerate until cold, about 1 hour.
In a large pitcher, stir together 6 cups cold water, the basil syrup and 1 1/2 cups lemon juice. Serve over ice; garnish with basil and lemon wheels.