If you need to drink water, drink. Yoga is all about feeling and not restricting right? So if you’re in a vinyasa and you really want that sip of water, go for it. Obviously, you don’t want to drink gallons of it during class, or use it as a distracting element to keep you from doing your least favorite poses, but the body needs what it needs.
If you’re going to bring a water bottle into class, make sure that it does not only not divert your attention from your practice, but that you’re also being mindful of the yogis around you. Many teachers discourage drinking water mainly because of the noises that can come with it.