Comparative study between bottled mineral and tap water in Italy.

In this work we compare the inorganic content of bottled mineral water, steadily increasing as a source of drinking water, and tap water which is often affected by intensive chemical treatment Bottled mineral water should be representative of the hydrogeochemical composition of groundwater, whereas tap water could derive from multiple sources such as groundwater or surface water including rivers and reservoirs. The data of this paper were collected within a project carried out by the EuroGeoSurvey Geochemistry Expert Group aimed at the characterization of groundwater geochemistry using bottled mineral waters purchased in supermarkets all over Europe which included also the analysis, for comparative purposes, of tap water. The comparison of two extensive databases of 69 elements on 157 tap water samples and 178 bottled mineral waters on Italian territory enabled the recognition of very wide ranges of variation in both databases. The elements with the highest variation are Y, Li, U, I, HCO 3 -, Be, Yb, Tm, Zr, Lu, F, and Cs in the bottled mineral database and Ga, PO 4 3-, Zn, Mg, Ti, Th, Cd, Pb, and Cu in the tap water database. The first group of elements in bottled mineral water includes elements with localized very high concentration due to prolonged interaction with unusual rock types, whereas the second group of elements in tap water includes elements that are released by corrosion reaction with the material of the distributing systems. Aside from these differences, tap water displayed a much more restricted range of variation for major ions compared to bottled mineral water because of quality guidelines imposed by Italian Law for selected major ions (Ca, Cl -, SO 4 2-).Some elements do not display statistically different distributions between the two databases (As, Cr, I, Li, Mo, Rb, Sr, Se, U, V) and for some of these (e.g., Cr and V) non-natural sources cannot be excluded in both databases (e.g. pipeline corrosion or container leaching). The spatial distribution of the ionic species provides similar information as far as the role of geology, groundwater condition and, additional sources is concerned. Among the elements displaying significant differences, Al, Cd, Cu, Fe, Ni, Pb and Zn are strongly enriched in tap water samples, whereas Be, Cs, Sb, Sn and Tl are significantly enriched in the bottled mineral water. The group of elements enriched in tap water is controlled also by corrosion processes, so their spatial distribution is random and virtually unrelated to geological or geochemical conditions. Among the elements enriched in the bottled mineral water group, Sb derives from PET container leaching, whereas the other elements likely derive from water-rock interaction.