I can't speak much to the specifics, because alcohol is against the rules at my university where i was an RA so I never dealt with this exactly. However, generally, I think you need to be as honest as you can be. You drink because it is legal for you to do so, You are not advocating drinking, and you are not advocating minors drink. Thats important to establish.
Be subtle and mature about your decisions, and that will reflect in how your residence view you.
As to facebook: putting pics of yourself up drinking is never smart. Employers and others look to facebook and its best to always represent yourself professionally.
-------
Do not abandon yourselves to despair.
We are the Easter people and hallelujah is our song.
Pope John Paul II