Perhaps if you read a little you'd see that this didn't come from the bottled water industry nor is there any evidence that bottled water manufacturers were claiming or even planing to claim this. The submission came from two doctors: Prof. Dr. Moritz Hagenmeyer and Prof. Dr. Andreas Hahn who think the EU is getting a little stupid with their regulations and I'm inclined to agree.
The article states "German professors Dr Andreas Hahn and Dr Moritz Hagenmeyer, who advise food manufacturers on how to advertise their products, asked the European Commission if the claim could be made on labels."
Did I miss something? Do you believe their request was disinterested?
Your statements are kind of cryptic as they don't appear to form any cogent argument defending the EU's decision. Do you simply believe that should an unbranded source of something exist (say Vitamin C) then there is no grounds for a branded product containing it make a health claim? (i.e. "Contains Vitamin C - which prevents scurvy").
If the unbranded source is readily available and consumed in every home, the promotion of the branded version with misleading therapeutic claims is debatable, ethically at least.
Here's a better analogy: Should I be allowed to sell oxygen tanks and claim that "regular breathing of significant amounts of oxygen helps fight hypoxia" ?
Or is it that you doubt the science behind the alleged benefit? That is, that water doesn't help you reduce the risk of development of dehydration. If so then your comments about "tap water" are even more strange as in that circumstance tap water also doesn't help you.
The science is weak, especially when the claim recommends "regular consumption of significant amounts of water". What is a "significant amount" ? Excess water intake does have detrimental health effects. Proactive drinking is recommended to prevent dehydration in some circumstances (lasting physical exercise, exceptional heat, to the elderly), but in general listening to one's thirst is adequate. Also, if someone actually suffers from dehydration, a significant water intake can be dangerous; if you want a simple advice, slowly chewing and eating a vegetable is a better bet.
I'm not saying the EU doesn't have more urgent things to deal with, but had I been asked to rule on the appropriateness of the claim, I would have reached the same conclusion.