01 - Place the watermelon cubes in a blender and blend until smooth.
02 - Pour the watermelon puree through a fine mesh sieve into a large pitcher to remove pulp, if desired.
03 - Add the freshly squeezed lemon juice and sugar or agave syrup to the pitcher. Stir until the sweetener dissolves.
04 - Add the cold water and mix well. Taste and adjust the sweetness or acidity as needed.
05 - Chill in the refrigerator for at least 1 hour, or serve immediately over ice. Garnish with lemon slices and fresh mint before serving.