A polite, "no, thanks" and perhaps shift the convo to something y'all learned, spent time on or [ ] that day. Shift to other people - and leave with a reasonable amount of time contributed. I bet you're not the only one who "ducks out early" to call their wife or kids, or because they don't drink either, or because they have to be polite but are on their way to a better job at another co and don't want to reveal anything.....so many reasons.
And, going to the area with a water bottle in hand is a great tool - you can drink it and your hands are full.