Bottled water costs substantially more than what comes from the tap but is not healthier for consumers, a study has suggested.

Researchers found the 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, it was reported.

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. It can cost up to thousands more.

“Water coming from U.K. taps is the most stringently-tested in the world,” said Prof Paul Younger, of Glasgow University.

“People think there must be something wrong with tap water because it is so cheap and plentiful. But from a safety and price perspective, tap water is better for you.

“If the bottle is accidentally opened or someone tampers with it, then it can easily get contaminated.”

Prof Younger, the author of "Water: All That Matters," added to the Daily Mail: “There's certainly a greater chance you could find something harmful in bottled water than from your taps.

“Ideally it should be drunk on the day it is opened, as it can easily pick up bacteria from someone's hands or face.”

It is estimated that Britons spend about £1.5 billion on bottled water each year. Experts say that we drink 33 litres of bottled water annually, whether ordinary mineral, fizzy, or 'purified' tap water”.

Market researchers Mintel have found that 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.

Sue Pennison of the Drinking Water Inspectorate, which audits household supplies, told the newspaper that out of more than four million samples of tap water last year, 99.96 percent passed strict standards.

She said: “Tap water is safe to drink, everything else is a personal lifestyle choice.”

But Jo Jacobius, director of British Bottled Water Producers, said all water available in Britain was “highly regulated and generally of good quality.”

Most bottled water companies test their products on a daily basis.

Natural bottled mineral water must come from an officially recognised underground spring, be bottled at source and cannot be treated or filtered.

Spring water must also be bottled at source, but it can be treated or filtered. Sourced from rivers, boreholes and springs, tap water is treated and put into supply or held through storage reservoirs.