Water, water everywhere but not a drop for free - or at least so it seems.

Did you ever imagine that you would buy a bottle of water from a vending machine and pay more than you do for a can of water with carbonation, caffeine and sugar?Evian, Naya and other bottled water machines, which are springing up all over the U.S., are just one more sign of the surging popularity of bottled drinking water. Last year Americans drank 3.4 billion gallons of the stuff.

What's the big attraction? What are you getting for your money that you don't get free from your tap? Well, probably water that doesn't taste or smell of chlorine - or anything else. And depending on where you live, perhaps cleaner water.

The federal government has similar safety standards for bottled water and municipal water supplies. There is actually little difference between the two after municipal water has been purified by a bat-tery of processes such as distillation, reverse osmosis, ozonation, deionization or filtration. Pure water is pure water.

The distinction is that bottled water is sealed as soon as it has been treated. Tap water, however, must travel to your faucet through a pipeline, where it may pick up contaminants such as the parasite cryptosporidium.

"The purity of tap water depends on the maintenance of your distribution system," explains Dr. Stephen Edberg, professor of laboratory and internal medicine at the Yale University School of Medicine.

Most distribution systems are fine, but pipes sometimes crack, Edberg says, which can lead to contamination. By contrast, the purity of bottled water can be controlled from the source to the bottle.

But whether you're concerned about safety or just want to avoid tap-water taste, you don't necessarily have to pay $2 a liter for the product of a pristine Alpine spring.

The no-name spring water you can buy at the supermarket for a buck or two a gallon has been treated for removal of surface contaminants, rendering it just as safe. The same is true of bottled waters that do not come from natural springs but from treated municipal water supplies. The label may not say where the water is from if the source is local, but the label must indicate the source if it is from out of state.