When your dog's water breaks, she has entered the first stage of labor. This is when her cervix relaxes and dilates, creating a passageway through which the pups will be born. This does not, however, mean she's going to start pushing them out right away. Throughout this first stage of labor, she'll appear restless and may seek solace in her whelping box until the second stage of labor begins.
Once her water breaks and her cervix dilates, your dog still has some time before beginning the abdominal contractions that will force out her puppies. This pre-whelping stage of labor typically lasts between 6 and 12 hours, during which time she'll seem nervous, and may pant excessively or throw up. Stay close by, because once her water breaks, she has half a day or less before she starts pushing out pups.