Combine fresh squeezed lemon juice, sugar, blueberries, and hot water in a blender. Blend until sugar has dissolved and berries are pureed.

Pour into a large pitcher, using a small sieve to remove the pulp. Add cold water, tear mint leaves and add, stir to combine, and chill in the fridge for an hour or so before serving.

Serve over ice. Use a small sieve to strain the mint leaves out at this point if you don't want them in your drink.