Purple Basil Lemonade

In this recipe, basil is ground with sugar to separate the oils. If you don't have a mortar and pestle, chop the basil, sugar, and about 1/4 cup water in a food processor or blender.
Combine 4 cups of water and juice in a large bowl. Put 1/2 cup basil and sugar in a mortar; mash with a pestle until a paste forms. Add the sugar mixture to the juice mixture; stir until the sugar is dissolved. Strain the mixture through a sieve into a bowl; remove any dry residue. Put 1 cup of ice in each of the 4 glasses. Pour about 1 cup of lemonade into each glass; garnish each serving with 1 sprig of basil.