In all seriousness, i have a bottle of this I've used because it just cleans better, but supposedly effective quite low temps, but no longer available, maybe it was bad for people:

http://www.pelicanparts.com/cgi-bin/...%252C%2520each

My guess BMW doesn't make it and it's this:

 

I've gone through an entire gallon in one day (100 miles) in bad weather. With the lights on, its seems that I must be dumping fluid somewhere because it lasts for over a week if I'm careful to turn off my lights before using the spray.

 

ya'll using the correct winter formula wiper fluid? I had regular fluid in and it started to freeze in this -10 windchill....i switched to winter formula and have been fine..you'll end up cracking the resirvoir if it freezes in there