Materials and methods

Data
The dataset used in this paper was derived from a hydrochemical study in Po Plain Italy (Conti et al. 2000). Our data re-use proposal was granted by the principal investigator via several emails. The data was chosen because we believe the hydrochemical values are similar with the occuring system in Indonesia. We have gathered 90 samples with 14 variables on each samples consists of: 11 samples of formation water and 79 samples of groundwater (Table 1 and Table 2). We have calculated the regression coefficients, presented as correlation table in the supplementary data table.
1 Variable description