Can the same tap water make some people sick and not others? i'm getting diarrhea from it but not my roommates. there is no fluoride added here btw.

Is it the water?: The diarrhea might be from some other cause, and not the water. That would be most likely given that you are the only one that is sick. You should discuss this with your doctor. You might need some testing. If you are still concerned about the water, then it might be useful to actually have the water tested.

Everybody is: Unique - metabolic system, digestive system, immune system ... . It sound more like something you perhaps ate earlier in the day. The Fluoride doesn't have any effect relative to your symptoms. Hope this helps.

Possibly: If you are new to an area the tap water probably has different amounts and different types of sediments, chemicals and bacteria in it than you are used to. As your body gets acclimated to the new water (approximately 7-10 days) the diarrhea should resolve. If severe or it doesn't resolve in a timely manner then you should see a doctor for an evaluation.