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