Mix together the water, sugar and cava. Leave to cool in the refrigerator for 2 hours.
Cut the Sapito melon in half, remove the seeds and cut the flesh into cubes.
Squeeze the ¼ lemon for juice and use the remainder for the lemon zest.
Using a blender, combine the Sapito with the Cava mixture and the lemon juice.
Put the mixture in the freezer for another hour.
Serve in glasses decorated with lemon zest and melon balls, to taste.