I like to make this drink in two parts. First prepare the watermelon juice. Add watermelon chunks, black salt and lemon juice along with water in a blender and blitz it to make juice. Pour this in serving glasses that already contains ice cubes. Next add guava pieces along with water, black salt and paprika to the blender and make juice. Pour this over the watermelon juice. Don't mix it, the color contrast makes it even more appealing. Serve it chilled.
You can use regular salt if black salt not available.Skip the paprika if you want.