2/3 cup fresh lime juice
1/2 cup sugar
1 1/2 cups raspberries (about 6 ounces), fresh or frozen (thawed)
3 cups sparkling water
1. Combine lime juice and sugar in a large pitcher, stirring to help dissolve the sugar.
2. Place berries in a fine-mesh sieve over a bowl. Use a rubber spatula to press on the berries, extracting the juice and some pulp while leaving the seeds behind. Stir the puree into the pitcher.
3. Just before serving, stir in seltzer. Serve over ice.
Make Ahead Tip: Prepare through Step 2, cover and refrigerate for up to 2 days.