In a one liter mason jar or container add the sliced cucumber and lemon. Pour the grapefruit balsamic over the cucumber and lemon and refrigerate for at least one hour or up to four hours. The longer it sits, the more pronounced the flavor of the fruit infusion. Strain and keep refrigerated and tightly covered for up to two months.
To serve, add 1-2 tablespoons of shrub (depending on your preference for sweetness) for 8 oz. of chilled sparkling water. Serve over ice if desired.
Makes between 16-32 servings depending on amount added to water or cocktails.