Final answer:
The nurse's priority when a client's water breaks is to assess the fetal heart rate to ensure the well-being of the unborn baby before proceeding with other interventions.
Step-by-step explanation:
When a client states, "My water just broke," the nurse's priority intervention is to assess fetal heart rate. The fetal heart rate provides immediate information about the unborn baby's condition after the amniotic sac ruptures and can indicate distress or well-being. The priority is not to administer oxytocin, insert a urinary catheter, or check cervical dilation and effacement, although these actions might follow based on the assessment.