Add the berries, honey, water, lemon juice, and mint to a blender (you can use an immersion blender). Mix on high speed until completely smooth. Taste and adjust for sweetness to suit you.
To serve, divide the lemonade base between six glasses and top with sparkling or still water. You can blend everything together if using still water.
1 litre (4 cups) water, sparkling or still
The lemonade base, without the added litre of water, will keep in a sealed container in the refrigerator for a couple of days.
Notes
Some mint, especially if you bought it from the supermarket, might not have as strong of a taste, or might be bitter. Adjust the amount added to suit your preference.