Add the blackberries, water, honey, and lemon juice to a blender or blending container (if using an immersion blender). Blend on high speed until very smooth and fully mixed. Check to make sure the honey is incorporated. This is your blackberry lemonade base.
Divide the base into glasses or add to a pitcher and top with the additional litre of cold water. Serve with ice if desired.
1 litre (4 cups) cold water
Notes
Sieve if you'd like: if you're not a fan of seeds, simply strain the mixture through a fine-mesh sieve before topping with the additional water. If your sieve isn't fine enough you can use cheesecloth or a nut milk bag.Sweeten to taste: I don't like drinks to be overly sweet and this is fairly tart. You might want to add more honey to your preference, or reduce it if your berries are very sweet.Storage: keep the base in a sealed container in the refrigerator for up to five days, or top with still water and refrigerate. If using sparkling water add it immediately before serving.Freezing: the blackberry lemonade base can be frozen for up to a month in an airtight container, or in single servings in an ice cube tray (remove and transfer to a container once fully frozen). Thaw in the refrigerator before serving with additional water.