Hello and thank you for your question.
Here is a great article on birthing puppies and what to expect, what to watch for and when to be concerned:
Dog's do not have their "water break" quite like a human. Each puppy has it's own amniotic sac that is removed by the mom after it is born. What we monitor in dogs is how long they have been straining and how long between puppies. You can see there that if she strains hard for over an hour with no puppy produced, or goes longer than 4 hours between puppies (when you know there are more inside) it is time to call the vet as there may be a problem.
I hope this helps, thank you for your question.