Combine the following ingredients in blender: 2 cups water, blueberries, honey, apple cider vinegar, ginger, optional spirulina and optional stevia.
Puree on medium speed until blueberry skins are teeny, about 50 seconds. Add lavender and blend briefly again, about 10 seconds.
Pour into tall 8-cup mason jar (see link below in Recipe Notes). Add final 4 cups water. Stir and leave out on the counter for a minimum of 4 hours, but preferably overnight.
Chill and serve.