In a large blender, combine the cubed watermelon, water, sugar, and lime juice. Place the lid on the blender and blend until smooth.
Pour over ice and serve immediately. Garnish with a lime wedge if desired.
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Notes
If you have a smaller blender, you may have to work in batches. Combine all of the watermelon water in a large pitcher and stir to combine after blended.
You can strain the watermelon water before drinking if you prefer.