Put your watermelon in a blender (like this one) and pulse until it's pureed perfection. You should have about 4 cups. Pour them through a mesh strainer and into a bowl. In a pitcher (like this darling one), whisk the water, lemon juice, and sugar until it's dissolved. Stir in the watermelon, then add ice. Chill in refrigerator until ready to serve. Garnish with mint or lime wedges!