1. Bring 1/2 cup water to a boil in a medium saucepan. Stir in sugar and grated lemon rind, stirring until sugar is dissolved; remove from heat. Stir in lemon juice and ice water.
Limeade: Substitute 1 Tbsp. grated lime rind for lemon rind and 1 1/2 cups fresh lime juice for lemon juice, and proceed with recipe as directed.