It is hard to imagine a bigger marketing fiasco than the launch of Coca-Cola’s Dasani bottled water. First, it emerged that the brand was nothing more than filtered tap water from Sidcup. Then the South London suburb was flooded by a burst water main. This week came the final insult: Coke announced a Europe-wide recall, after finding high levels of bromate, which is linked to cancer, in its water.

It was as if the gods were angry. Perhaps it was the price mark-up — a mere 300,000 per cent. In truth, it is pretty unlikely that drinking a few bottles of Dasani will do any damage to anything apart from your bank balance. Bromate is classified as a possible human carcinogen and that means there’s no hard evidence that it has ever given anyone cancer. All the data are from mice and rats, and even if it does affect people, you’d have to drink gallons for years on end to reach dangerous levels of exposure. At 95p for half a litre, you’d be bankrupt long before you fell ill.

But even if Dasani has fallen victim to an exaggerated scare, there is delicious Schadenfreude in Coca-Cola’s plight. The bottled-water craze, after all, rests on just such a scare in the first place. Its popularity relies on the erroneous perception that it’s healthier than tap water. Dasani’s slogan — “pure, still water” — sought to capitalise on this. It has been hoist with its own petard.

The bottled-water market is a modern form of alchemy in which cheap raw materials can be transmuted into gold. Many more varieties of aqueous snake oil are still out there.

Penta water is probably the most outrageous example. This claims to be “biologically restructured by high-energy sound waves” so that water molecules form into smaller clusters. According to the company’s website, these enter cells more easily than large clusters, hydrating the body more effectively.

It all sounds very scientific but that doesn’t stop it being nonsense. Even if the Penta treatment can shrink the molecule clusters, they’d last only a few trillionths of a second before being smashed up as they collide with each other. In any case, size isn’t everything. Water molecules enter cells not in clusters but one at a time. Penta fans such as Gwyneth Paltrow and Cameron Diaz are being blinded by pseudoscience.

Then there are those waters that trumpet liberal doses of added oxygen. This is another promotional ruse. It aims to exploit a vague feeling that oxygen is good for us. Yes, we can’t live without it — but we get everything we need from breathing the air.

Fish get their oxygen from the water but human beings don’t have gills. Even if we did, we’d have to swim in the stuff, not swallow it, to derive any benefit. One breath contains several orders of magnitude more oxygen than one could possibly absorb from a drink. Our lungs, not our stomachs have evolved to do this job.

As Bob Park, of the American Physical Society, says: “An attempt to extract the oxygen you need from water is called ‘drowning’.” The bottled-water industry thrives on these myths — and on the outdated notion that drinking tap water is risky. It isn’t. Tap water is so well treated these days and safety standards are so strict that it is about as safe as any water can be.

There’s every reason to pay for Evian or Malvern — and even Dasani or Penta — if you like the taste or the image. But the notion that they are any better for you than turning on the tap is a mirage.

Mark Henderson is the Times science correspondent

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