In a blender or food processor, blend the fresh blueberries until they form a smooth puree.
Strain the puree through a fine mesh sieve to remove any skins, reserving the blueberry puree.
In a large pitcher, combine the water, freshly squeezed lemon juice, and sweetener. Stir well.
Add the blueberry puree. Then taste and adjust the amount of sweetener to suit your taste preferences. The sweetness of the berries may vary, so adjust accordingly.
Tear the basil leaves and add them to the pitcher, lightly bruising them with a spoon to bring out the flavor. Then grate the lemon zest directly into the pitcher and stir well.
Fill glasses with ice cubes and pour the blueberry lemonade over the ice. Garnish each glass with a few fresh blueberries and a slice of lemon, and serve.
Notes
Please note that the nutrition data given here is a ballpark figure. Exact data is not possible.