London: Though health-conscious fitness enthusiasts are never seen without bottled water, and it is subject to less stringent safety tests than tap water, the bottled variety is much more likely to be contaminated, says a new study.

Bottled water costs more than tap water but is more likely to become a source of infection, the Daily Mail cited a study by market researchers Mintel as saying.

On average, Britons 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 than tap water.

But what consumers do not realise is that tap water is 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.

In 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.

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

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