## 6 Probability of Groundwater
### Drinking Water Quality Index (DWQI)  
The WQI method was used to evaluate the general groundwater quality for use as drinking water. Using the quantile classification approach in GIS, the study region was divided into potable, moderately potable, and non-potable zones based on the DWQI. The DWQI results show that, in January 2020, 48% of the groundwater in the study area was potable and 47% of the area contained groundwater in the non-potable class. In January 2021, 75% of the study area was potable groundwater, and 22% was non-potable groundwater according to the DWQI (Table S3). The maps of the spatial distribution  
\begin{table}
\begin{tabular}{l l c c c c c} \hline \hline \multicolumn{1}{c}{**Parameters**} & \multicolumn{1}{c}{**Category**} & \multicolumn{1}{c}{**Range**} & \multicolumn{2}{c}{**Jan-20**} & \multicolumn{2}{c}{**Jan-21**} \\ \cline{3-6}  & & & **In. No** & **In.\%** & **In. No** & **In.\%** \\ \hline \multirow{3}{*}{pH} & Not potable & \textless{}6.5 & Nil & - & Nil & - \\  & Permissible & 6.5–8.5 & 40 & 100 & 39 & 97.5 \\  & Not potable & \textgreater{}8.5 & Nil & - & 1 & 2.5 \\  & Acceptable & 0–500 & 14 & 35.0 & Nil & - \\ TDS (mg/L) & Permissible & 500–2000 & 15 & 37.5 & 27 & 67.5 \\  & Not potable & \textgreater{}2000 & 11 & 27.5 & 13 & 32.5 \\  & Acceptable & \textless{}75 & 28 & 70.0 & 6 & 15.0 \\ Ca\({}^{2+}\) (mg/L) & Permissible & 75–200 & 8 & 20.0 & 27 & 67.5 \\  & Not potable & \textgreater{}200 & 4 & 10.0 & 7 & 17.5 \\  & Acceptable & \textless{}30 & 25 & 62.5 & 9 & 22.5 \\ Mg\({}^{2+}\) (mg/L) & Permissible & 30–100 & 11 & 27.5 & 21 & 52.5 \\  & Not potable & \textgreater{}100 & 4 & 10.0 & 10 & 25.0 \\  & Acceptable & \textless{}250 & 24 & 60.0 & 16 & 40.0 \\ Cl\({}^{-}\) (mg/L) & Permissible & 250–1000 & 12 & 30.0 & 19 & 47.5 \\  & Not potable & \textgreater{}1000 & 4 & 10.0 & 5 & 12.5 \\  & Acceptable & \textless{}200 & 33 & 82.5 & 31 & 77.5 \\ SO\({}_{4}\)\({}^{2-}\) (mg/L) & Permissible & 200–400 & 2 & 5.0 & 7 & 17.5 \\  & Not potable & \textgreater{}400 & 5 & 12.5 & 2 & 5.0 \\ NO\({}_{3}\)\({}^{-}\) (mg/L) & Acceptable & \textless{}45 & 38 & 95.0 & 19 & 47.5 \\  & Not potable & \textgreater{}45 & 2 & 5.0 & 21 & 52.5 \\  & Acceptable & \textless{}1 & 38 & 95.0 & 37 & 92.5 \\ F\({}^{-}\) (mg/L) & Permissible & 1–1.5 & 2 & 5.0 & 3 & 7.5 \\  & Not potable & \textgreater{}1.5 & Nil & - & Nil & - \\ TH as CaCO\({}_{3}\) & Acceptable & \textless{}200 & 21 & 52.5 & Nil & - \\ (mg/L) & Permissible & 200–600 & 11 & 27.5 & 17 & 42.5 \\  & Not potable & \textgreater{}600 & 8 & 20.0 & 23 & 57.5 \\ \hline \hline \end{tabular}
\end{table}
Table 2: WHO [31] and BIS [54]-based potable water quality.  
of the DWQI (Figure 3a,b) show that the northern and southern coastal regions and the southern and central coastal regions, followed by the northwestern portions, each contained non-potable groundwater during both time periods. The groundwater quality improved in January 2021 compared to January 2020. This is due to the fact that the near-surface aquifers of the study area were recharged with fresh rainwater. Raising awareness of rainwater harvesting systems among the population of the study area and making their use mandatory in all buildings will improve groundwater recharge and ultimately increase the availability of freshwater for drinking [56].