Whether or not you bring a mini-fridge to your dorm room is really about personal preference and your eating habits. Some people go to the dining hall or a local store/restaurant/on-campus-convenience-store/cafe every time they are hungry. Some people prefer to preserve some snack foods and drinks in a fridge in their room. I don’t know your style – I rarely used my mini-fridge freshman year.
A lot of students use Brita pitchers, but there are sinks and/or water fountains in every residence hall, if you’re fine with that.
Yes… you can get bottled water on campus. You can buy it at cafes (there are 4) or at Father’s, or a few other places. You can also pick it up with to-go meals at the dining halls. RPI is like a small city.