Just about every American house has plenty of tap water available anytime. So why has bottled water consumption doubled in the last decade?

On average, American consumers drink about 28 gallons of bottled water annually per person. One reason: many people seem to believe that bottled water is actually safer than tap water. There’s some credence to the claim: some local newspaper investigations have shown all manner of contaminants in supposedly treated municipal water.

But after a four-year review of the bottled water industry and the safety standards that govern it, the National Resources Defense Council concludes that bottled water is no cleaner or safer than water from the tap.

“An estimated 25 percent or more of bottled water is really just tap water in a bottle - sometimes further treated, sometimes not,” says a NRDC report.

Who monitors quality?

The feds. But while U.S. Food and Drug Administration standards for contaminants take into account the Environmental Protection Agency’s tap water standards, the two standards aren’t identical. Some standards for bottled water are stricter than for tap, such as those for fluoride and lead.

But some are not. Bottled-water companies may not disinfect or even test for parasites such as Cryptosporidium or Giardia - requirements for municipal tap water. The FDA says bottled water sources are unlikely to harbor the parasites.

So what’s the problem?

Water bottles are often made of polyethylene terephthalate (PET #1), a product of crude oil. “Making bottles to meet Americans’ demand for bottled water requires more than 1.5 million barrels of oil annually, enough to fuel some 100,000 cars for a year,” according to the Earth Policy Institute.

Transporting bottled water comsumes energy, adding carbon dioxide to the atmosphere, contributing to global warming.

Plastics are generally recyclable, but we are less likely to recycle water bottles. The Container Recycling Institute claims that a high percentage of plastic water bottles used in the United States become garbage or litter.

What are the alternatives?

Increasingly, restaurants serve free, filtered local tap water instead of expensive bottled water. This “drink local” movement benefits environment and customers by avoiding the environmental costs of producing and transporting bottled water long distances. The downside: Banning bottles can mean a significant loss of revenue for establishments used to marking up bottled water prices.

Sources: Consumers Union, Earth Policy Institute, U.S. Food and Drug Administration