I would totally recommend using it. Rock salt adds the perfect saltiness to balance the sweet and tart tastes in this cocktail juice. It is easily available in Indian stores, on Amazon and at other stores too. Called rock salt, kala namak or Himalayan pink salt, this salt is a MUST-HAVE for the recipe for the flavor. If you absolutely cannot find it, replace with some chaat masala or regular salt. The flavors will definitely vary but might work to some extend.