Nasty Water Spots (apparently from Windshield Washer Fluid)

[GannyCy]

Has anyone had any issue with water spots from windshield washing fluid (fluid from BMW dealer or the factory)? I used my wipers and windshield washing fluid while driving a few times to remove bug smears, and apparantly the fluid migrated to the driver side and passenger side windows (due to wind from driving) and left water spots that I can't remove. I found this suprising since I would assume that what ever fluid BMW uses that is should not be "hard" and leave spots than can't be removed with glass cleaner. What specific fluid does BMW use? Should it be replaced with a different type of fluid to protect the glass?

[dannym]

I guess they could have used hard water to dilute the washer fluid? I think I read somewhere that BMW use Sonax washer fluid. I was told by BMW UK that I should only use their branded fluid as the cheaper versions can block the washer jets and won't be covered under warranty. I always use filtered or bottled water in my car to avoid water spots.