1. Combine 4 cups water and juice in a large bowl. Place 1/2 cup basil and sugar in a mortar; pound with pestle until a paste forms. Add sugar mixture to juice mixture; stir until sugar dissolves. Strain mixture through a sieve over a bowl; discard solids. Place 1 cup ice in each of 4 glasses. Pour about 1 cup lemonade into each glass; garnish each serving with 1 basil sprig.