Movies and TV shows are fond of showing pregnant women in public places suddenly standing in a puddle of amniotic fluid. The fact is, the bag of waters, or amniotic sac usually breaks after contractions have begun, and sometimes just before delivery.
The water doesn’t always gush out, either. Though the amniotic sac holds 2 ½ - 3 cups of fluid, whether it comes out all at once Hollywood style, or little by little, depends on whether you have a tear or a rupture. Some women aren’t even aware that their water has broken, mistaking the slow leak for discharge common in late pregnancy.
I hope that helps, please post any questions you might have!