Vinegar and water in my book. if that doesn't get it call up Unique Autosports.

 

I have seen polishes that specifically mention water spot removal. These were polishes meant for painted surfaces. If it's safe for paint ,it should be safe for glass. Look around a little and see if you can find something.

 

For the type of water spots that won't come off using conventional means, I've used Bruce's GSR (Glass Stain Remover). The product is abrasive and has the look and consistency of potting clay (mud). Again, I only reserve this option when the glass is so heavily stained that it's like looking through dried milk on your windshield.

 

Just washed my truck yestarday, and now I have water spots all over my windows, and they aren't coming out!!! *grumbles*