01 - In a saucepan, combine the chopped rhubarb, 1 cup of water, and sugar. Bring to a boil over medium heat, then reduce to a simmer and cook for 10 minutes, or until the rhubarb is soft.
02 - Strain the rhubarb mixture through a fine mesh sieve into a bowl, discarding the solids. Allow the rhubarb syrup to cool.
03 - In a pitcher, combine the cooled rhubarb syrup, freshly squeezed lemon juice, and 3 cups of cold water. Stir well.
04 - Add the fresh basil leaves to the pitcher and let the mixture steep for at least 30 minutes in the refrigerator before serving.
05 - Serve over ice, garnished with additional basil leaves if desired.