It's possible to get oral herpes type 1 this way. It's just as likely, or more likely, that you'd get a cold, the flu, strep, etc., this way, and it's still flu season in many places. Make your roommate get his own water bottle. You aren't over-reacting by asking this. Many people without OCD don't want to share drinks, utensils, toothbrushes, etc.
Plz I shared my water bottle for a year till now and all the time he touches his mouth while.dri nking he is my roommate for 1 year now