I've been drinking Powerade Zero. A couple of 22 oz. containers along with a couple of Protein shakes equate to 66 oz. It takes a bit to work up to that. I'm on week 4 and just now beginning to manage the 64 oz. recommendation. The Powerade is flavored and goes down easier than Water for me. Good luck!
I've gotten used to the Premier Protein shakes. They're available at the Target pharmacy. I believe they come in chocolate, strawberry, banana, and vanilla flavors. Good news is that they have 30g of protein. Bad news is that it's an acquired taste. I prefer only the chocolate.