I just got Get To Work when it was on sale, and my doctor sim stops in the middle of patient exams to get water or soda even when he's FULL. I cancel it out when I see it, but he drops the Examine Patient action I just queued to go fetch MORE water. This is seriously annoying, espeically since all these actions take so much time already. He hasn't enough time in a day to treat 3 patients!
I've got this problem as well. Sims always mixing drinks and then leaving them on the bar to spoil. Sims drinking water when they visit the apartment and leaving the glass out to spoil (who would've thought that *water* could spoil? After an apartment visit, just about every flat surface in the apartment has glasses all over it!
I've never had Sim stop what they were doing to go get a drink as reported by @Felicat82 I wonder if your actions are cancelling prematurely and then the game fills in with a trip to the water fountain?
