just realised what i wrote it is ment to say two pints of water. *sorry*
hi when i went for a ultrasound i had to drink to pints of water so they could see the scan.
when i went for my level 2 u/s, i did not have to drink anything. in fact, the tech offered to let me use the bathroom before we got started.
i am a tech, and it is 40oz!! 21 will not fill your bladder full enough and they will make you drink more and wait once you get there so drink the 40 1 hr before your appt and you will be fine!
21 oz an hour before.
Good luck!
It also depends on how many weeks gestation you are. When you are 35 weeks +, it is ok with less water. Around 20 weeks or earlier, I would drink the 40 ounces. Good luck to you!