According to a university study, bottled water is also much more likely to be contaminated or become a source of infection, the Daily Mail reported.
Bottled water, the benefits of which are so valued that it costs up to 1,000 times more than what comes out of the tap, is subject to far less stringent safety tests than tap water and far from being healthier, to a new study has claimed.
The warning suggests that much of the ore than 1.5-billion-pound people from Britain pay for bottled water each year in the belief that it is better for us is spent mistakenly.
On an average, we drink 33 litres of bottled water annually, whether ordinary mineral, fizzy, or 'purified' tap water.
Almost a quarter of people who drink bottled water at home say they do so because they believe it is better for them than tap water, according to market researchers Mintel.
But what these consumers may not realise is that tap water must be checked daily under a rigorous inspection regime.
It also contains trace amounts of chlorine that prevent the spread of anything harmful like bacterial infections.
By contrast, makers of bottled water are only required to undertake monthly testing at source. Once filled and sealed, a bottle of water might remain in storage for months before it is sold. Bottled water contains no disinfecting additives like chlorine.
After a bottle of water is opened it has no way of remaining sterile, and so must be drunk within days.