Pour chopped watermelon into a blender. Blend until pureed.
Line up 4 (25 ounce) bottles with flip top lids or other air tight bottles.
Pour ½ cup pureed watermelon and 2 tablespoons maple syrup into each 25 ounce bottle.
Using a funnel, pour freshly made homemade kombucha into each 25 ounce bottle leaving 1-2" head space.
Let bottles sit out (at 75° - 85°) 3-5 days, making sure to pop the lids each day to let out the pressure of the carbon dioxide. Taste each day to test its flavor and fizziness.
Notes
Use freshly made homemade kombucha that has not been refrigerated yet.Use maple syrup if your watermelon isn't as sweet as you'd like.