I can't tell you how many times I've heard this from many of the athletes I've had the opportunity to work with. Maybe it's my training... but I can't be wrong (slight sarcasm), so I am guessing it's not. I quickly give them an answer to their comment, going off about how it comes down to movement, nutritional intake, and psychological states.
I saw this today regarding water and flexibility at CorePerformance.com:
I've also told athletes this same thing for years, but is all this water recommendation just another patch on a leaky ceiling? What about all the s**t we eat on a daily basis. It's an absolute "Catch 22" on hydration states. High fructose corn syrup and all the other simple corn-derived carbs that infiltrate most of our diets are just sucking all the water out of our cells. Not to mention all the f-ing with insulin levels that go on because of these simple carbs.
While I'm at it... dairy products fuel the fire as well, evaporating our tissues with simple sugars. Paints a pretty bleak picture when you think about all the foods we consume that contain corn and dairy. This discussion could go for miles...
Here's a good video overview I saw at Conditioning Research the other day regarding diet and health as it's viewed from a paleolithic perspective. Something to think about.
You can only patch-up a ceiling so much, before you need a new ceiling. So yes, drink more water, but it may not drown out all the problems.