In reading the BBC news awhile ago, an interesting article popped up. The title read, Fake holy water warning 'working.' So what does that mean? In the UK they were doing inspection to see if vendors were selling 'fake' holy water because this variety of water can be filled with arsenic and nitrates. The 'fake' water is described as Zam Zam (from a well in Mecca) water but it isn't really from there. The article states, "The Kingdom of Saudi Arabia forbids the commercial export of genuine Zam Zam, so we have no idea of the true source of the water which ends up on the streets of the UK."
I should think people concerned with buying 'fake' holy water only have more problems than they can handle. At least the 'real' (note the quotation marks) holy water won't poison you if you drink it.
See the article at the BBC website.