Spatial variation of stable hydrogen and oxygen isotopes in tap water in Brazil

Compared to global models, regional water isoscapes have increased spatial coverage sampling to better represent the territory patterns and decrease the uncertainty of isoscapes. Here, we present the first tap water isoscapes for Brazil. We collected 575 tap water samples and analyzed for δ¹⁸O and δ²H using a pyrolysis technique coupled to isotope ratio mass spectrometer for isotope ratio determination. We performed multiple linear regression models between stable isotopes of tap water and values extracted from geographical and climatic variables. Then we fitted semivariograms to perform an ordinary kriging interpolation for spatial prediction of tap water δ¹⁸O and δ²H values. The observed δ²H ranged from -63.9 ‰ to 15.4 ‰, and the δ¹⁸O ranged from -9.2 ‰ to 3.7 ‰. The δ¹⁸O and δ²H tap water isoscapes showed a clear and noticeable spatial pattern as a gradient of increasing stable isotope values from the southwest to the northeast of the country. The tap water isoscapes evidenced the main meteorological systems: the Intertropical Convergence Zone (ITCZ) and the South Atlantic Convergence Zone (SACZ). In conclusion, the isotopes of water in Brazilian tap water are consistent with the primary meteorological systems that deliver precipitation to the landscape.