I have seen Potassium chloride, Magnesium Sulfate, and calcium hydroxide in a number of different bottled waters (maybe same bottler, different labels?).
At any rate, just a quarter teaspoon of potassium chloride is equal to about 6 potassium supplement capsules as the highest potency you can find is 99mg due to FDA restrictions. FDA - Consumers best interest??? I do not think so, more like big pharma protectors.