8 tablespoons super-fine sugar (adjust if too sweet when using a naturally sweeter watermelon), divided
4 very thin lime slices, halved into half moons, divided
Add the watermelon and the water to a blender, and puree until smooth. Divide the mint leaves, sugar and lime slices among 8 glasses and muddle the ingredients. Add ice to each glass and pour in the watermelon agua fresco. Stir and serve.