The influence of geochemical processes and quality of groundwater in a rural tract of Damodar Valley region were investigated. The study has distinguished the groundwater as fresh, soft to moderately hard and mainly CaHCO3 type. The paired samples student’s t test shows the significant seasonal variations of pH, HCO3−, and Fe. Amphoteric exchange has lessened HCO3− concentration in post-monsoon which subsequently has caused to drop pH. Quite the reverse, the monsoon precipitation has triggered the additional release of Fe from iron-bearing sediments. The contaminant Cl− is from the domestic wastewater as is evidenced by field observations. The inter-variable relations, cation and anion mechanisms, and mineral saturation indices reveal that the dissolutions of silicate and carbonate minerals are the primary sources of major ions in groundwater. The chloro-alkaline indices showed the role of ion exchange too in water chemistry. The R-mode factor analysis also successfully identified two dominant processes regulating water chemistry—geogenic sources (Ca2+, Mg2+, Na+, and HCO3−) and anthropogenic inputs (mainly Cl−). The groundwater is found unsuitable for drinking at 82 and 93% of wells in pre- and post-monsoon seasons, respectively mainly due to elevated Fe content. The water from more than 90% of wells is appropriate for irrigation uses. The study recommends the proper treatment of contaminated water for consumption and measures to protect the groundwater from the waste water infiltration.