The hydrogeochemistry of bottled mineral water in São Paulo state, Brazil

The composition of groundwater primarily reflects hosting lithologies, and according to other studies, natural bottled water can be used as a simple means of groundwater sampling. This study aims to establish compositional relations between the groundwater of six aquifers of São Paulo state, Brazil and host igneous, metamorphic and sedimentary silicate rocks. Bottled water drawn from sixty-eight different sources was analyzed to apply a source-rock deduction. One-fourth of the bottled water was resampled to determine the concentration of rare earth elements (REE). The mineralization of the water is low (TDS = 7-332 mg/L, median = 79 mg/L), its pH is mostly circumneutral and the hydrogeochemical characteristics of the majority of samples indicates Na-Ca-HCO3 type. Silicate weathering (possibly of plagioclase), is the main mineralization process identified for all six aquifers. Minor processes identified include the weathering of gypsum and ferromagnesian minerals and cation exchange. From the REE content we split the set of samples into two subgroups. The subset with higher ∑REE (529-10,932 ng/L) is acidic (pH < 6) and includes less mineralized water from shallow sources. A second set is compositionally more heterogeneous and grouped samples with lower ∑REE values (0.67-100 ng/L). Concerning regulated constituents, only two specimens present either high U (98 μg/L) or Cr (73 μg/L) values. Twenty-three samples show nitrate values (NO3-N > 0.7 up to 9.0 mg/L) that are attributed to non-lithological sources. Overall, these results indicate that the sampled bottled mineral water satisfactorily represents the groundwater in corresponding aquifers.