The benefits of bottled water are so valued that it costs up to 1,000 times more than what comes out of our taps.

London - It’s the one accessory that no health-conscious fitness enthusiast is seen without.

And the benefits of bottled water are so valued that it costs up to 1,000 times more than what comes out of our taps.

But far from being healthier, the bottled variety is subject to far less stringent safety tests than tap water.

It is also much more likely to be contaminated or become a source of infection, according to a university study.

The warning suggests that much of the £1.5-billion-plus Britons pay for bottled water each year in the belief that it is better for us is spent mistakenly.

On 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 such as 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 such as chlorine.

After a bottle of water is opened it has no way of remaining sterile, and so must be drunk within days.

Professor Paul Younger of Glasgow University said: “Water coming from UK taps is the most stringently tested in the world.

“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,” added Prof Younger, who is the author of Water: All That Matters.

“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.”

Batches of bottled water have had to be removed from supermarkets shelves because of questions over contamination.

In 1990, Perrier had to withdraw millions of bottles worldwide after traces of benzene were found in the water.

And in 2004, Coca-Cola launched Dasani, which was ‘purified’ tap water taken straight from mains supplies.

But within weeks hundreds of thousands of bottles were recalled after it emerged the purification process may have contaminated the water with a possibly carcinogenic substance. Tap water supplies have also been compromised in the past. In 1988, aluminium sulphate was added to the wrong treatment tank, polluting the drinking water in Camelford, Cornwall.

Sue Pennison of the Drinking Water Inspectorate, which audits household supplies, said 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.”

Jo Jacobius, director of British Bottled Water Producers, said all water available in the UK is “highly regulated and generally of good quality”.

She added that most bottled water companies test 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 via storage reservoirs. - Daily Mail