In a blender, combine the diced watermelon and sliced cucumber. Blend until smooth.

Strain the mixture through a fine mesh sieve into a large pitcher to remove any pulp.

Add the sparkling water, fresh lime juice, and honey or agave syrup (if using) to the pitcher. Stir gently to combine.

Fill glasses with ice cubes and pour the Cucumber Melon Splash over the ice.

Garnish each glass with fresh mint leaves before serving.