Geochemical evaluation of bottled groundwater from crystalline aquifers located in the south and southeast of Brazil

Abstract

The mechanisms related to rock-water interaction are important to understand the quality of groundwater. The chemical composition of 38 brands of bottled water from crystalline aquifers located in the South and Southeast regions of Brazil was determined for understanding the rock-water interaction processes. The results indicate that the water samples show different stages of rock-water interaction, which can be measured by the concentration of HCO₃^- ion. The exploratory analysis indicates that low mineralized water, probably from recent recharge, is of mixed type. On the other hand, more mineralized water is of bicarbonate type, ranging from sodium to calcium, and with a high proportion of magnesium. Despite the different compositions of the rocks that make up the studied aquifers, calcium-magnesium silicates, predominantly represented by hornblende, are the ones that mainly affect the water composition. Sodium and part of the calcium in water are derived from the hydrolysis of plagioclase, whereas potassium is derived from the dissolution of potassium feldspar.