The only reason to buy bottled water is for the convenience (and possibly taste). In Illinois, homeowners who have their own wells often buy drinking water due to quality problems with their well water. But if you get your drinking water from a public water supply, that water is regulated by the Environmental Protection Agency (EPA), which has developed drinking water standards for more than 100 contaminants. Bottled water, on the other hand, has been defined as food and is regulated by the Food and Drug Administration (FDA), using different standards than EPA. FDA's regulations are defined as Current Good Manufacturing Practices (CGMPs), such as using sanitary conditions, protecting water sources, and analyzing for a smaller set of contaminants than EPA requires. This is not to say that bottled water is unsafe, but its quality is no better than tap water.

The main difference between bottled water and tap water is the bottle. And there has been a concern that the bottles, whether plastic (usually polyethylene terephthalate (PET)) or glass, may leach contaminants into the water. That was the focus of a recent study published in the journal Applied Geochemistry [Reimann et al., 2010. Bottled drinking water: water contamination from bottle materials (glass, hard PET, soft PET), the influence of colour and acidification. Appl. Geochem. 25:1030–1046]. They tested 126 bottles of three types (glass, hard PET, soft PET) and five colors, and analyzed for 57 different elements, several of which are regulated by EPA (As, Ba, Be, Cd, Cr, Cu, Pb, Se, Tl, and U). Antimony (Sb) was the main contaminant found in PET bottles, lead (Pb) in glass. Concentrations increased temporally for most of the elements for the duration of the experiments (150 days). Higher concentrations were found in dark colored bottles vs. clear bottles, and in carbonated water (lower pH) vs. uncarbonated. The highest values they measured for regulated contaminants were 0.45 μg/L for Sb (EPA standard is 0.6 μg/L), 0.61 μg/L for Pb (EPA standard is zero), and 0.06 μg/L for chromium (EPA standard is 100 μg/L). Although any detectable Pb is above the standard, EPA defines 15 μg/L as the “action level” for Pb, which means that “if more than 10% of tap water samples exceed the action level, water systems must take additional steps to control Pb (and copper) levels.”

Based on this study, neither PET or glass bottles appear to contaminate the water within, although you may not want to store it for long periods of time. However, you should remember that producing bottles requires energy. The Pacific Institute estimated that, in 2006, the bottled water industry in the U.S. used the equivalent of more than 17 million barrels of oil in the production of bottles, produced more than 2.5 million tons of carbon dioxide in the bottling process, and took 3 liters of water to produce 1 liter of bottled water. From both a water quality and environmental point of view, the best choice is to buy a reusable metal water bottle and fill it from the tap.