Ultrasound Questions

Amanda
So my first ultrasound is next Sunday the 19th, I'm 6w4d today so I'll be 7w6d that day, and I am a first time mom. The lady at the place told me to chug 32oz of water 15 mins before coming in. Why am I do this? Is the purpose to bloat me up? Also, I'm assuming this is a regular ultrasound since no one even told me what a transvaginal ultrasound was until I found ladies on here talking about it. Any and all help would be appreciated, thanks ladies! 💕