8 cups water, divided
5 cups peeled, cubed, and seeded watermelon
1/2 cup white sugar, or more to taste
1/3 cup lime juice, or more to taste
Combine 1 cup water, watermelon, and sugar in a blender; process until smooth. Pour into a large pitcher; stir in lime juice and remaining 7 cups water. Taste; adjust sugar or lime juice. Refrigerate until chilled, about 1 hour.