Many years ago, when I was a small child, we went to a part of the Middle East where there was minimal medical care. My parents were briefed before we left by our company doctor, who told them that a fizzy drink from a can or bottle with an added pinch of salt provides the right proportions of salt, glucose and water to rehydrate in hot weather. Since bottling and canning plants use sterilised water, there was no risk of picking up any bugs. To this day, fizzy pop doesn’t taste quite right to me without the added salt!