My T always offers a beverage...I typically turn her down. Sometimes, I bring my own, and just once I took her up on the offer of water, when I simply hadn't had anything to drink all day.

I find having a drink during session to be distracting. I seem to use it as a way to stop talking about difficult stuff...ya know, it's getting difficult, get a drink, deflect, etc. So, I try to avoid it unless I'm just really thirsty or have a sore throat or something.