Powder the sugar. Add watermelon and sugar in your blender and blitz it. Strain it.
Squeeze the lemons for the juice.
Add chilled water, lemon juice, watermelon juice, rock salt and ice cubes in a pitcher. Mix it well.
Pour it in glasses, add more ice cubes and garnish it with mint to serve.
Adjust sweetness according to your taste.
You can add few leaves of mint while you blend watermelon to take out its juice.
If you like the pulp of watermelon in your lemonade, deseed, juice it and use it.