Some years ago, for health reasons, I took a break from drinking any alcohol. However, at this time, my work friends loved to drink. Some of them too much. Heading off to a bar was just the common way to socialise after work. Then all of the questions would start, why aren't I drinking something alcoholic. This was obvious because there was the habit of people taking turns to buy the drinks. So my not drinking and health often became a topic. So I understand where you are coming from. It becomes tiring having to justify a choice or requirement.
Solution? Grow a tougher skin and not concern yourself with other peoples' concerns about your preferences or needs with fluid intakes.
Non participation is a very interesting social exercise, especially with intoxicants of any sort. Peoples' behaviour changes and yourself more or less remains as is and you observe the shifts in conversation and behaviour. You start to feel like an anthropologist.
Yes, being familiar with the rituals of the cultural you are engaged in are important, if you want to interact with people. If those rituals include coffee, tea, alcohol, whatever, knowing how to prepare these things be an added social lubricant.
@leoplaw You're right, it is interesting to observe the experience without participating. Luckily, the more my friends drink, the less they care that I'm not drinking (as far as "Here, try this!", "Try that!", "Are you suure you don't want such-n-such?", "You don't like it??") because they're having way too much fun!
Yes, your friends after a point have more important things to do. Who's buying the next round? ;-)