In my experience vinegar, and any other over the counter liquid calcium remover will remove minor hard water deposits the only problem it take days and weeks of rubbing & scraping rather then hours.
There are 3 major levels of water stains:
(1) Simple water stains that are on the outside from spill overs or short term exposure. These can be removed with vinegar with some hard rubbing over a short period of time.
(2) Embedded mineral deposits can only be removed with abrasives that are harder then calcium / magnesium but softer then glass OR harder then glass provided the abrasive is so fine that the scratches to the glass are microscopic and appear perfectly clear to the naked eye. For this there are glass buffing compounds you can buy, or what I use is Turtle Wax Heavy Duty Rubbing Compound which has a soluble paste made up of very fine volcanic ash, also a glass so its about neutral with glass.
(3) Glass damage from years of exposure to oxidizing air/water mixed minerals where the minerals actually replace the top layer of glass, and or scratches. All of which can only be repaired or removed with abrasives harder then glass starting with such things as course sand paper and working your way down to progressively finer materials until it is polished out.