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.
Bring rhubarb, cold water, sugar, and ginger to a simmer in a 4- to 5-quart pot over moderate heat, uncovered, stirring once or twice, then simmer 1 minute. Remove from heat and let steep, uncovered, 1 hour.
Pour mixture through a large fine-mesh sieve into a large bowl, gently stirring but not pressing on solids (discard solids; you will have about 6 cups syrup). Chill syrup completely, about 45 minutes.
Serve syrup in glasses over ice with a splash of sparkling water.
