Regarding hydration:
While plain water is the best option, if you know you aren't going to drink it, then any means of getting enough hydration, even if that is flavored water with 5 or 10 calories or whatever is better than going without. My clinic also specifically mentioned Vitamin Water Zero, protein water and the option of some drink mixes like Crystal Lite. There is often much higher compliance with flavored water than there is with plain water for people to reach their intake. That is just the reality. I'm sure my doctor or surgeon would love for me to drink water and only water, but that's not my reality. For whatever reason even if I have a bottle of water next to me, I won't drink as much if I have some ice tea (decaf) sweetened with stevia or something else like that.
If we were all perfect people, we'd just be drinking water, but we aren't perfect and we have our different tastes. Water is the best choice, by far, but not at the cost of getting dehydrated. No one should feel guilty about drinking what they need to maintain hydration. We want to make the best choices possible throughout this journey, but some choices won't be perfect.
"....we will chase perfection, and we will chase it relentlessly, knowing all the while we can never attain it. But along the way, we shall catch excellence." Vince Lombardi
In my opinion:
Best option: water
Second best option: water flavored with the essence of natural fruit, like lemon, lime, etc.
Third: non-caffeinated, non-carbonated zero-calorie drinks sweetened with stevia or sugar alcohol
The rest comes after that, including flavored powders, pre-mixed vitamin and protein waters, etc.