We're here to tell you that cantaloupe has a lot going for it. Fragrant, sweet, and a touch creamy, it is a perfect pairing for the basil-infused syrup and tart grapefruit juice that it is blended with for this refreshing, agua-fresca-style cooler.
In a small heatproof bowl, pour 1/2 cup boiling water over sugar and basil; stir until sugar has dissolved. Let cool completely, about 20 minutes. Strain syrup into a blender; discard basil.
Add cantaloupe, grapefruit juice, and 1 3/4 cups cold water; blend until smooth. Strain through a fine-mesh sieve.
Serve over ice, garnished with a basil sprig, or refrigerate in an airtight container up to 3 days. If using vodka, stir a shot (1-ounce) into each glass before serving.