Prepare the Blueberries: In a blender, combine the fresh blueberries and a cup of water. Blend until smooth.
Strain the Mixture: Place a fine-mesh strainer over a bowl or pitcher and pour the blended blueberries through it to extract the juice. Press gently with a spoon or spatula to get as much juice as possible.
Mix It Up: In a large pitcher, combine the strained blueberry juice, freshly squeezed lemon juice, and sugar. Stir well to dissolve the sugar.
Add Water: Pour in the remaining cold water and mix thoroughly. Taste and adjust the sweetness if needed by adding more sugar or water.
Chill: Refrigerate the lemonade for at least an hour or serve immediately over ice.
Serve: Pour the blueberry lemonade into glasses filled with ice, garnish with lemon slices and a sprig of mint if desired, and enjoy the refreshing sip!