Edit: I noticed that since the April 13 update, Sims also seem to be drinking milk and orange juice autonomously even when Hunger is in the green.
Back in December 2014, a rule from the update has been added to prevent Sims from drinking from the fridge autonomously but it appears that this rule is broken notably as of GTW/version 1.5.
It happened in my game where I had two Sims, Rebecca and Ashley. Rebecca made a Sunset Valley and then I put it on the fridge, later I spotted Ashley drinking the Sunset Valley despite the rule stating that Sims will no longer drink from the fridge. Unfortunately, EA partially altered the rule. While it was supposed to prohibit Sims from drinking from the fridge autonomously, it doesn't stop them from attempting to make drinks or drink any drinks and they'll do this regardless of Hunger levels.
To get around this problem, I moved the Bar to the Household Inventory so that the Sims would not make any drinks. I only take it out to do Rebecca's daily task or to make potions. I've made a thread at The Sims forums discussing this issue.
This is one of the bugs that didn't get fixed in the March 26 update. However, Sims drinking from the fridge autonomously might be a bug.
and with the new update from June 2016 where they can drink water from the tab, they do that all the time too + getting milk and orange juice and autonomously start mixing drinks as well. I wish they didn't do that.
My sims are drinking water now from kitchen and bathroom sinks, and they will do this for no reason. Sometimes they will grab a glass right after they have eaten. My pregnant sim will drink water until her bladder nearly explodes.
Maybe there's a good reason to have a sink in some expansion pack somewhere that I don't have, but for me, there's no benefit to having a sink, so the houses I play don't have them. They just waste time. So, as a workaround, maybe consider getting rid of your sinks.
i don't mind if they drink from time to time, i mean, who doesn't. but the way it is now... it's getting out of hand.
