I don't think I can

Drink a gallon of water a day!!! I'm going to get my 3D/4D photos Done next weekend and they want me to drink a gallon a day for a week. Ugh that's like impossible for me, I can barely drink 50 oz 
Is that much really necessary? I mean I know they want me to because it makes it better to see the baby but damn, that's a lot of water!!