Comment This is to prevent abuse. (Score 3, Informative) 815
Of course Water does fight dehydration, but so does Coka-Cola, Orange Juice as well as most drinks containing large quantities of Water.
The EU is simply refusing generic statements on products that don't have any distinguishing meaning compared to other products in the same class.
McDonalds might want to put "Two BigMacs will give you 70% of your daily calories need", which may be true, but it is highly misleading.
The whole purpose of this EU law is that consumers can trust the statements made by manufacturers are both true and distinguishing for that product compared to others in the same class.