In a blender, blend fresh watermelon until smooth.
Strain using a cheesecloth to yield 1 ¼ cups of watermelon juice.
Add the watermelon juice, filtered water, lime juice, ginger bug, and maple syrup to a sterilized, pressure-safe swing-top bottle.
Leave about 1 inch of headspace at the top.
Gently swirl to combine all ingredients evenly.
Seal the bottle and allow it to sit on the counter to ferment.
Fermentation times may vary depending on temperature, but typically take 2–3 days.
Burp the bottle daily to release pressure buildup.
Refrigerate immediately once fermentation is complete.
