Add blueberries, basil leaves, honey, lemon juice, and water into a small saucepan.
Heat on medium for 2-3 minutes until the berries soften.
Gently mash berries and basil with the back of a spoon while heating.
Remove from heat and pour the mixture through a fine mesh strainer to catch solids. Press with a spoon to extract juice.
Let the syrup cool for at least 10 minutes.
Fill a glass with ice cubes.
Pour 2-3 tablespoons of the blueberry-basil syrup over the ice.
Top with sparkling water.
Stir gently to combine.
Garnish with extra basil leaves and blueberries, if desired.