Plus those water bottles are the 32oz Gatorade bottles. The amount I drink depends on the diaper I'm wearing- Super Dry Kids can only do about 2 bottles, Rearz can get 4 and then some, but I'll just feel uncomfortable before they start leaking.
I haven't worn in public in a long time. Last year, I wore Abena M4s as my main diaper. They have a pretty good capacity, especially for their price range, provided you aren't going out of your way to completely saturate them. They're on the thicker side, but they don't swell up very much when wet. I wore them in public a few times with loose-fitting clothing, so there wouldn't be a noticeable bulk. If noise is a concern, there's cloth-backed versions as well as plastic. I wore to a midterm once, classes and a movie (two diapers, plus one to sleep in) on the same day, and to two of my finals. So I'd definitely recommend M4s (or S4s, or L4s, depending on your waist size), or ABU Preschools (also have plastic and cloth backed versions). Both have great price-to-performance and are generally discrete enough to wear in public.
I changed my habits this year since I had a roommate, so I'd just order small samples of premium ABDL diapers and wear them in private when I had the chance, which is why I use them as heavily as I do. I've tried Bellisimos, LittlePawz (my faves), SDKs, Crinklz, and Rearz Safaris. These diapers aren't meant for public wear, though. They're extremely thick, and will already make you walk awkwardly while dry. They swell up a ton when wet and force you to waddle. I can't even walk down the hallway in my dorm to refill my water bottle, let alone go out in public (fortunately my floor is pretty quiet, and there's a sink not far from my room). The plastic backing is much louder than on Abenas, and I always get ABU diapers with the baby-fresh scent.