A lot of US municipal water is full of junk you don't want. Plastic probably isn't better though. If I had a nice well I would never touch the stuff.
Tap water is much safer than bottled water.
Depends on where you are. In most of the USA, that's correct. But in places like Florida, you'd rather die of thirst than drink the tap.
Bottled water usually has that nasty side effect of those chemicals from the plastic seeping into it. Yum!
Could be -the flavor of water in long-reused plastic bottles seems to support this notion- but it has more to do with the fact that bottled water, like herbal remedies, isn't weighed down by stringent bureaucratic red tape standards, like actual medicine. Sure, they go overboard. Umbrage mentioned fluoride additives in tap water as a negative point, which is most likely accurate. And then we have shit like what started this thread in the first place - which is hilarious not only in the way it defies common sense, but also (and even more so) because the word "dehydration" literally means "loss of water," so these thin-lipped suit-monkeys are *literally* saying that water is a magical element, since its presence does not counteract its absence. It would seem that water both eliminates and creates its own existence... simultaneously! One would believe we have stumbled upon God, as made manifest on this transient vale. And if you look at water on a large enough scale, this is true; the planet can't lose or gain water, after all

All the same, when faced with a choice between two opposite extremes, it would be pretty stupid to choose that of "no precautions at all" over that of "too many precautions." Except for the ubermensch, of course.
As for living in Florida, I'd rather die of anything than be there in the first place.