Add 3 cups watermelon, ½ cup syrup, ¼ cup water, and 1 tbsp lime juice to a high-speed blender. Blend until smooth, pausing to push the watermelon sorbet down if the blades get stuck.
Transfer the watermelon sorbet to a metal loaf tin or other freezer-safe container and place in the freezer.
Repeat these steps with the remaining ingredients, then serve immediately or store covered in the freezer for up to 1 week.