Ads suggest it’s pure H2O, implying that it’s less contaminated by pollutants than what flows from the tap.

So Is Tap Water Really Better?

Recent tests commissioned by the Environmental Working Group (EWG), a nonprofit environmental organization based in Washington, D.C., show that 10 bestselling brands of bottled water contained "a surprising array of chemical contaminants...at levels no different from those found in tap water."

A total of 38 different contaminants were found, ranging from bacteria and fertilizers to drugs and industrial chemicals. All of these contaminants have also been reported in tap water in some parts of the country, and they don’t necessarily make water unsafe to drink. But with an average of eight contaminants per brand, it’s clear that some bottled water is no purer — and in some cases maybe less pure — than many American municipal water supplies.

The International Bottled Water Association countered that the EWG’s report contained "false claims and exaggerations" and maintains that bottled water meets federal standards for drinking water quality.

So what’s a water drinker to do? Get the facts and then decide for yourself.

Fact No. 1: An estimated 45 percent of bottled water comes from ordinary municipal water supplies. Many bottlers begin with municipal water, filter it and label their product as "purified" water. "Spring" water must come from an underground spring. "Mineral" water must come from an underground source and contain at least 250 parts per million of total dissolved minerals. "Artesian" water must come from a well that taps into an aquifer.

While all this may sound good, keep in mind that all municipal water supplies are filtered,

and many come from springs or aquifers and contain enough minerals to be called mineral water. If you’re curious where your bottled water comes from, check the label, visit the company’s Web site or call their 800 number to ask. Click to the Web sites of Aquafina (owned by Pepsi) and Dasani (Coca-Cola) revealed that they contain filtered tap water.

Fact No. 2: Bottled water is less regulated than tap water. The Environmental Protection Agency (EPA) regulates tap water and requires municipal water systems to test annually for contaminants and publish the results. The Food and Drug Administration (FDA) regulates bottled water but has no testing or publication requirement and rarely inspects bottled water plants.

If you’d like to view the latest test results for the water that flows from your tap, contact your municipal water supplier to ask for a copy. You can also have your water tested. The EPA’s Safe Drinking Water Hotline (800-426-4791) can provide the names of reputable laboratories. Then, the lab sends you test tubes. You fill them from your tap, and the lab sends you a report. Cost varies based on the number of contaminants involved, but figure on spending $75 to $150.

Fact No. 3: Chemicals may leach from plastic bottles into bottled water.

This is controversial. Some experts say there is little, if anything, to worry about. But several studies, including a 2002 report by Polish researchers and a 2006 study by Japanese scientists, show that chemicals from plastic bottles leach into bottled water, notably formaldehyde, acetaldehyde and acetone.

Fact No. 4: Home water filters are cheaper than bottled water.

OK, so maybe you don’t like the taste of the tap water in your area, or the test results reported to the EPA were less than supreme. Water filters can help at a fraction of the cost of bottled water. Typical American tap water costs less than half a cent per gallon. Bottled waters cost around $3.79 per gallon — that’s 2,000 times more. If you drink eight glasses of bottled water a day, it can cost more than $1,000 per year. For most consumers, it maybe be cheaper to install a water filter under your sink and drink home-filtered tap water. Keeping in mind that home filters must be cleaned and serviced regularly, otherwise the contaminants they trap might be reintroduced into your water.

Fact No. 5: Plastic bottles are bad for the planet.

Americans drink nine billion gallons of bottled water a year, packaged in the equivalent of about 35 billion one-liter plastic bottles. It takes a great deal of energy to manufacture those bottles.

It takes even more energy to fill those bottles and ship them, often thousands of miles, to market. In the end, the vast majority of empty water bottles end up in landfills.

So give some thought before you buy your next bottle of water. Some people like the convenience, especially when they’re out and about. Others prefer the taste. But if your primary concern is purity, you might do just as well turning on the tap.