Place blueberries in a colander and spray some vinegar all over. Drizzle some baking soda and gently smear it all over the berries. Leave them for 5 minutes.
Rinse them well under running water. Repeat the rinse several times until the water runs clear.
Add them to a blender jar along with lemon, sweetener and 3 cups ice (or 2 cups chilled water and 1 cup ice)
Blend until smooth, add more ice or water if needed for a thinner consistency.
Pour to serving glasses and serve blueberry juice immediately. If you let it sit, it will set like a jelly due to high pectin.