In a large pitcher, lightly muddle the blueberries with the simple syrup until the berries release their juices and turn the syrup deep purple.
Stir in the fresh lemon juice and vodka until well combined.
Add the cold water and half of the ice, then stir gently to chill and dilute slightly.
Taste and adjust: add more simple syrup for sweetness or more lemon juice for extra tartness if desired.
Fill glasses with the remaining ice and pour in the blueberry lemonade.
Garnish with lemon slices, a few blueberries, and mint sprigs. Serve immediately.
Notes
For a lighter spritz, top each glass with a splash of club soda. Make it non-alcoholic by skipping the vodka and adding an extra 1.0 cup of cold water. Chill the pitcher up to 24 hours in advance; add ice and garnishes just before serving.