So, you took a drink, right there? It wasn't written in the script, but you wanted to take a drink of water, right there, after your third line?
You better have a damn good reason.
If the author wanted you to drink there, they would've written "HE TAKES A DRINK OF WATER." But they didn't, did they?
Drinking water there could be brilliant. It could be the best decision anyone has made all damn day in the scene, but there better be a reason you made that choice, as in you can back it up and not just seem like an actor using a crutch to get through the scene.
If you choose an action, there's gotta be a reason behind it, and, of course, that reason will change with each scene. But it better be there, and it better be good.