Combine the Granulated Sugar (1 cup) with one cup Water (1 cup) in a small sauce pot. Bring the mixture to a gentle boil and cook 2 minutes. Remove from the heat and pour into a heat safe glass. Place in the fridge to cool.
Add half the Watermelon (4 cup) and another Water (1 cup) a blender and puree until smooth. Strain the mixture through a fine mesh strainer set over a large bowl. Discard the watermelon pulp.
Again, add the remaining Watermelon (4 cup) and another Water (1 cup) to the blender, then puree until smooth. Strain the mixture through a fine mesh strainer set over a large bowl. Discard the watermelon pulp.
To the large bowl add the remaining Water (2 cup), Lemon Juice (1 cup) and the sugar water from the fridge. Whisk to combine and then taste. Add more water if it is too sweet for your liking.
Pour into glass jugs and store in the fridge. Before drinking, make sure to shake the lemonade up.
To make the slushies, Add the Ice (4 cup) and Lemonade (1 1/2 cup) to a blender and blend until nearly smooth but slightly chunky. Add the Fresh Mint Leaves (1 tablespoon) or basil if using, taste and add more lemonade if desired.