In a saucepan, heat up water and sugar and bring to a boil until the sugar has dissolved. Set aside and let it cool.
Blueberry puree
Blend the blueberries together with half a deciliter (3 tablespoons) of water and the lemon juice. Mash the blended blueberries through a sieve with a tablespoon to get as much juice through as possible.
Serving
Mix the simple syrup and the concentrated blueberry juice and serve it with ice cubes, lemon slices and a few fresh blueberries on top. Drink the lemonade as it is, or mix it up 1:1 with water or sparkling water.