Start by chopping the watermelon into small chunks, ensuring they are seedless or de-seeded for a smooth blend. Place the chunks into a blender.
Juice the lemons using a citrus reamer or a manual juicer, then strain the juice through a fine mesh sieve to remove pulp and seeds. Pour the fresh lemon juice into the blender with the watermelon.
Add honey to the blender if desired for extra sweetness. Secure the lid and blend the mixture on high until smooth, about 30 seconds, until the watermelon is fully liquefied and has a vibrant pink color.
Place a fine mesh sieve over a large pitcher and pour the blended mixture through it, pressing gently with the back of a spoon to extract as much liquid as possible, leaving pulp behind. Discard the solids.
Add ice cubes to the strained juice, then stir well to chill. Serve immediately in glasses garnished with lemon slices or small watermelon wedges for an eye-catching presentation.
