To call this bracing pink drink a rhubarb-infused ginger ale doesn't do it justice; it's much less syrupy-sweet and more cooling. The slightly tart flavor of rhubarb pairs well with lush picnic dishes.
Cooks' notes:
·Syrup can be made 3 days ahead and chilled, covered. Add sparkling water just before serving.
·Syrup keeps, frozen, 3 months.