Cut 500 grams of watermelon into small cubes and remove the seeds.
In a blender, add the watermelon cubes and blend until smooth. Strain the juice through a fine mesh sieve to remove any pulp.
In a large pitcher, add 10-12 fresh mint leaves and 2 tablespoons of sugar. Muddle the mint leaves and sugar together using a muddler or the back of a wooden spoon to release the mint flavor.
Add the juice of 2 limes (approximately 4 tablespoons) to the pitcher.
Pour the strained watermelon juice into the pitcher and mix well.
Fill the pitcher with 500 ml of soda water or sparkling water and stir gently.
Fill glasses with ice cubes and pour the watermelon mojito over the ice. Garnish with a slice of lime, a sprig of mint, and a small watermelon wedge.