In a medium saucepan, combine the blueberries, sugar, and water. Bring to a boil over medium heat, stirring occasionally until the sugar has dissolved and the blueberries have burst, about 5-7 minutes.

Remove the saucepan from heat and let the mixture cool for about 15 minutes.

Once cooled, strain the blueberry mixture through a fine-mesh sieve into a bowl or pitcher, pressing down on the solids to extract as much juice as possible. Discard the solids.

In a large pitcher, combine the blueberry syrup with the freshly squeezed lemon juice. Stir well to combine.

Just before serving, add the sparkling water or club soda to the pitcher and stir gently to combine.

Serve over ice and garnish with fresh mint leaves if desired.