We've spiked this lemonade with white rum to make a refreshing summer cocktail, but you can omit the alcohol. One batch will completely fill your blender, so if you need more, make multiple batches rather than doubling or tripling the recipe.
Blend cherries (including pits) in a blender at low speed until skins have broken down enough to brightly color liquid (some of pits will be coarsely chopped). Pour through a sieve into a 4-quart pitcher, pressing on and discarding solids. Add lemon juice and sugar, to taste, stirring until sugar is dissolved.
Pour 3 tablespoons white rum, if using, into each of 16 tall (10-ounce) glasses filled with ice. Add 1/2 cup cherry lemonade to each and top off with sparkling water.
Cooks' note: Sour cherry lemonade can be made 1 day ahead and chilled, covered.