Bmw is notorious for having soft paint which easilly gets stone chips. On my Z3 and '03 Z4, I had so many stone chips regardless of how careful I was. I would stay back from trucks etc. When I got my '06 Z4, I did not drive it away from the dealer until I had the 3M clear bra installed. When I traded it in, it looked as good as new.
I don't know why when I took delivery of my '10 Z4, I did not opt to have the 3M applied. I drove my new car less than 100 miles and got my first stone chip on the front bumper. I immediately made an appointment to have the chip fixed and the 3M applied. My front bumper, 1/3 of the hood, and the backs of the mirrors are covered. You can barely see it unless you are on top of the car. Anyway, I can drive worry free on the highway now and I haven't got any more chips.
I don't have any water spots that you guys are talking about though.