British researchers found bottled water costs substantially more than what comes from the tap but is not healthier for consumers.
Bottled variety is subject to far less stringent safety tests than tap water and is much more likely to be contaminated or become a source of infection.
While tap water must be checked daily under a rigorous inspection regime, by contrast, bottled makers are only required to undertake monthly testing at source, it was claimed.
Tap water also contains trace amounts of chlorine that prevent the spread of anything harmful such as bacterial infections.
But once filled and sealed, a bottle of water might remain in storage for months before it is sold and contains no disinfecting additives such as chlorine.
After a bottle of water is opened it has no way of remaining sterile and so must be drunk within days.