The alcohol of choice typically drank by women who have to fit into a wedding dress and cannot afford to gain any calories from real beer. Thus, they drink bridesmaid's beer (water).
Annie: Hey Jill, you want to go to a frat party tonight? I hear there is going to be a lot of alcohol!
Jill: Remember Annie, I'm going to be in my sister's wedding, so I can only drink Bridesmaid's Beer!