The type of ultrasound exam will determine whether you need to drink water for the test. If the exam is an abdominal ultrasound, the patient does not need to drink water. A pelvic ultrasound requires at least 40 Oz of water 1 hour prior to the appointment time. The full bladder serves as a window to see your pelvic organs (i.e. uterus, ovaries, or prostate). Without a full bladder, it is difficult to see them.