How to Make It
Combine sugar; water; celery seed; chopped celery; and the rind, peeled in strips, of lemon in a saucepan over medium-high heat. Bring to a boil, stirring until sugar dissolves. Remove from heat; steep 1 hour. Strain syrup; discard solids. Cool completely. Stir 4 tsp. syrup into 1 cup (or more, depending on desired flavor) seltzer water. Store syrup chilled up to 2 weeks.