They Won't Remember That You're Not Drinking.

Making it a point to tell people that you're not drinking isn't necessarily the best strategy, and the reason is often very simple: they don't care.  In fact, the do worse than not care.  They aggressively don't care.  So ignore such statements.  Not to mention that it is almost always awkward to bring up not-drinking with a colleague or casual friend.  In some ways, your own sobriety should be cherished and protected.  There's no need, I think, to go telling everyone.  There's no need to prove a point to anyone but yourself.

In that respect, it is okay to make small excuses for the sake of social politeness, rather than dropping a non-drinking bomb that might just get ignored, or worse, damage your own reputation.  Parenthetical: Not drinking is a sign that drinking was/is a problem, and for most semi-casual conversations, wherein all participants are assumed to be in good standing socially and whatnot, telling someone that you are not-drinking is like advertising a mental problem, and will not necessarily be seen in a good light.  There's simply no need.

And if you do confide in someone that you're not drinking, because you think that she/he is close enough to know, be prepared for him/her not to remember.  Not drinking doesn't have to be a big deal.  Tell yourself.  Not others.