In a medium saucepan combine blueberries, sugar, and water.  Stir until the sugar is dissolved and bring the mixture to a boil over medium/high heat. Lower the heat to medium/low. Cook until the blueberries have burst, releasing their juices and the liquid is syrupy, about 7-10 minutes.

Remove from heat and strain the mixture into a glass pitcher, mashing the blueberries to release their liquid. You can discard the blueberries, save for another use, or toss the mashed berries into the pitcher.

To the pitcher add the blueberry simple syrup, freshly squeezed lemon juice, sugar, vanilla extract and water.  Stir to combine, adjusting the sugar as needed.

To serve:

Add a few ice cubes to an 8oz glass. Pour about ½ cup of lemonade and top with seltzer. Garnish with a lemon slice or blueberries if desired.