The Environmental Working Group (EWG) commissioned a study of the quality of 10 domestic brands of bottled water. The ten brands were purchased from eight different states and the District of Columbia, then sent to the University of Iowa's Hygienic Laboratory for analysis. Samples were also sent to the University of Missouri for further analysis. You can read about the methodology of the tests here.
Municipalities are required to test for contaminants every year and then to make the results of those tests available to the public. Check the website of your municipality to find out what's in your tap water. The bottled water industry has no such requirement.
The EWP's study concluded:
Altogether, the analyses conducted by the University of Iowa Hygienic Laboratory of these 10 brands of bottled water revealed a wide range of pollutants, including not only disinfection byproducts, but also common urban wastewater pollutants like caffeine and pharmaceuticals (Tylenol); heavy metals and minerals including arsenic and radioactive isotopes; fertilizer residue (nitrate and ammonia); and a broad range of other, tentatively identified industrial chemicals used as solvents, plasticizers, viscosity decreasing agents, and propellants.
Read the study. Stop buying and using bottled water. Today.