Hooking up, for better or for worse, is a part of the college program for many people and it is something that you will hear about in passing on break, on the bus, or just walking around the complexes. I think it's safe to say that if you are at least in a two bedroom or more apartment you will have at least one person who will have company over for those purposes (be it a one night stand, a program length "partner", or bf/gf). Talk to your roommates about it, but remember, what they do is their business so long as you're not a witness to it and it doesn't affect any of your belongings.
What I'm about to say I'm dead serious about. If you REALLY want to avoid hook up culture, go on facebook and see if there are any of the Mormon missionary students doing the program. My friend from back home got placed in an apartment with 3 of them randomly and they self enforced a no alcohol, no girls in the apartment, no swearing, no drugs set of rules.