**5.3 Analytical techniques**

The collected groundwater samples from the field were analyzed for chemical variables, using the standard water quality methodology of the American Public Health Association [10]. The chemical variables include pH, electric conductivity (EC), total dissolved solids (TDS), calcium (Ca2+), magnesium (Mg2+), sodium (Na+ ), potassium (K+ ), bicarbonate (HCO3 − ), chloride (Cl− ), sulphate (SO4 2−), nitrate (NO3 − ) and fluoride (F− ). The pH and EC of the groundwater samples were measured in the field, using a portable pH meter (60510-ISE, YSI Pro plus) and EC meters (60530-ISE, YSI Pro plus). The TDS was calculated from EC adhering to the procedure of conversion factor adopted by Hem [14]. The rest of the chemical variables were determined in the laboratory immediately after the groundwater sampling. A summary of the analytical procedures is listed in **Table 2**. All concentrations of chemical parameters are expressed in milligrams per liter (mg/L), except pH (units) and EC (μS/cm at 25°C).
