XZIEX atmospheric water generator

London

IT'S summertime, and odds are that at some point during your day you'll reach for a nice cold bottle of water. But before you do, you might want to consider the results of an experiment I conducted with some friends one summer evening last year. On the table were 10 bottles of water, several rows of glasses and some paper for recording our impressions. We were to evaluate samples from each bottle for appearance, odor, flavor, mouth, feel and aftertaste - and our aim was to identify the interloper among the famous names. One of our bottles had been filled from the tap. Would we spot it? We worked our way through the samples, writing scores for each one. None of us could detect any odor, even when swilling water around in large wine glasses, but other differences between the waters were instantly apparent. Between sips, we cleansed our palates with wine. (It seemed only fair, since water serves the same function at a wine tasting.)

The variation between waters was wide, yet the water from the tap did not stand out: only one of us correctly identified it. This simple experiment seemed to confirm that most people cannot tell the difference between tap water and bottled water. Yet they buy it anyway - and in enormous quantities.

In 2004, Americans, on average, drank 24 gallons of bottled water, making it second only to carbonated soft drinks in popularity. Furthermore, consumption of bottled water is growing more quickly than that of soft drinks and has more than doubled in the past decade. This year, Americans will spend around $9.8 billion on bottled water, according to the Beverage Marketing Corporation.

Ounce for ounce, it costs more than gasoline, even at today's high gasoline prices; depending on the brand, it costs 250 to 10,000 times more than tap water. Globally, bottled water is now a $46 billion industry. Why has it become so popular?

It cannot be the taste, since most people cannot tell the difference in a blind tasting. Much bottled water is, in any case, derived from municipal water supplies, though it is sometimes filtered, or has additional minerals added to it.

Nor is there any health or nutritional benefit to drinking bottled water over tap water. In one study, published in The Archives of Family Medicine, researchers compared bottled water with tap water from Cleveland, and found that nearly a quarter of the samples of bottled water had significantly higher levels of bacteria. The scientists concluded that "use of bottled water on the assumption of purity can be misguided." Another study carried out at the University of Geneva found that bottled water was no better from a nutritional point of view than ordinary tap water.

Admittedly, both kinds of water suffer from occasional contamination problems, but tap water is more stringently monitored and tightly regulated than bottled water. New York City tap water, for example, was tested 430,600 times during 2004 alone.

What of the idea that drinking bottled water allows you to avoid the chemicals that are sometimes added to tap water? Alas, some bottled waters contain the same chemicals anyway - and they are, in any case, unavoidable.

Researchers at the University of Texas found that showers and dishwashers liberate trace amounts of chemicals from municipal water supplies into the air. Squirting hot water through a nozzle, to produce a fine spray, increases the surface area of water in contact with the air, liberating dissolved substances in a process known as "stripping." So if you want to avoid those chemicals for some reason, drinking bottled water is not enough. You will also have to wear a gas mask in the shower, and when unloading the dishwasher.

Bottled water is undeniably more fashionable and portable than tap water. The practice of carrying a small bottle, pioneered by supermodels, has become commonplace. But despite its association with purity and cleanliness, bottled water is bad for the environment. It is shipped at vast expense from one part of the world to another, is then kept refrigerated before sale, and causes huge numbers of plastic bottles to go into landfills.

Of course, tap water is not so abundant in the developing world. And that is ultimately why I find the illogical enthusiasm for bottled water not simply peculiar, but distasteful. For those of us in the developed world, safe water is now so abundant that we can afford to shun the tap water under our noses, and drink bottled water instead: our choice of water has become a lifestyle option. For many people in the developing world, however, access to water remains a matter of life or death.

More than 2.6 billion people, or more than 40 percent of the world's population, lack basic sanitation, and more than one billion people lack reliable access to safe drinking water. The World Health Organization estimates that 80 percent of all illness in the world is due to water-borne diseases, and that at any given time, around half of the people in the developing world are suffering from diseases associated with inadequate water or sanitation, which kill around five million people a year.

Widespread illness also makes countries less productive, more dependent on outside aid, and less able to lift themselves out of poverty. One of the main reasons girls do not go to school in many parts of the developing world is that they have to spend so much time fetching water from distant wells.

Clean water could be provided to everyone on earth for an outlay of $1.7 billion a year beyond current spending on water projects, according to the International Water Management Institute. Improving sanitation, which is just as important, would cost a further $9.3 billion per year. This is less than a quarter of global annual spending on bottled water.

I have no objections to people drinking bottled water in the developing world; it is often the only safe supply. But it would surely be better if they had access to safe tap water instead. The logical response, for those of us in the developed world, is to stop spending money on bottled water and to give the money to water charities.

If you don't believe me about the taste, then set up a tasting, and see if you really can tell the difference. A water tasting is fun, and you may be surprised by the results. There is no danger of a hangover. But you may well conclude, as I have, that bottled water has an unacceptably bitter taste.

Tom Standage, author of "A History of the World in Six Glasses," is the technology editor of The Economist.