yup, what mrsnelson2010 said. and a baby can't survive well in the womb with a diminishing amniotic supply, so they usually keep you, and if your labor isn't progressing they will get it to progress via medication.
They keep you..because once your water breaks baby must be delivered within so many hours because of risk of infection.
Yes they will keep you to monitor you and the baby. My water slowly broke little by little and I called the doctor and they said to come in. Shortly thereafter my contractions started.
When mine broke I stayed home until 2 hours later when my contractions got bad! And then of course they kept me. But if you go right after it breaks they will probably keep you