A study was conducted to evaluate the hydrochemical processes controlling the water quality variations and to determine the water type of groundwater in Rajshahi City, Bangladesh, for drinking purposes. A total of 120 shallow and deep tubewell water samples were collected in pre- and post-monsoon seasons during the year 2008–2009 and analyzed for various physico-chemical parameters. The results of the analyses show that water samples were slightly alkaline to neutral pH. The average concentrations of Pb in all samples for the post-monsoon season were above the WHO's guideline for drinking water. For both seasons, arsenic levels exceeded the drinking water standard in 25% of groundwater samples and lead (Pb) levels exceeded in about 60% samples which contained elevated levels (>0.01 mg/L). The major cationic and anionic orders of dominance were unusual, being Ca2+ > Mg2+ > Na+ > K2 > Fe3+ > Pb2+ > Zn2+ > Cu2+ > As (total) > Cd2+ and HCO3− > Cl−> SO42− > NO3−, respectively. The study reveals that the water type of the groundwater was calcium bicarbonate (Ca-HCO3). Thus overall results suggest that groundwater quality of the study area was not suitable for drinking purposes without treatment especially for Pb and As.
Keywords: analysis, drinking water, groundwater, post-monsoon, pre-monsoon, quality