Groundwater quality monitoring for assessment of pollution levels and potability using WPI and WQI methods from a part of Guntur district, Andhra Pradesh, India

Assessment of pollutants and groundwater quality has attracted much attention worldwide as it is directly linked to human health. In view of this, groundwater samples were collected from a part of Guntur district, Andhra Pradesh, India, to assess groundwater pollution levels and groundwater quality, using Water Pollution Index (WPI) and Water Quality Index (WQI), respectively. Groundwater chemical composition results indicated that groundwater quality was characterized by alkaline and very hard categories with Na+ > Mg2+ > Ca2+ > K+: HCO3 $$^{ - }$$ - > Cl $$^{ - }$$ - > SO42 $$^{ - }$$ - > NO3 $$^{ - }$$ - > F $$^{ - }$$ - facies. TDS, TH, Ca2+, Mg2+, Na+, K+, HCO3 $$^{ - }$$ - , Cl $$^{ - }$$ - , NO3 $$^{ - }$$ - , and F $$^{ - }$$ - were above the recommended threshold limits in 100%, 100%, 35%, 100%, 100%, 100%, 100%, 95%, 85%, and 75% of groundwater samples, respectively, for drinking purposes. The geochemical diagram showed base exchange water type (Na+–HCO3 $$^{ - }$$ - ) in 50% of groundwater samples resulting from weathering and dissolution of plagioclase feldspars under the influence of soil CO2 and ion exchange process. The remaining groundwater samples showed saline water type (Na+–Cl $$^{ - }$$ - ) due to the influence of evaporation, sewage sludge, septic tank leaks, irrigation-return flows, agrochemicals, etc. Ionic relationships of Ca2+/Na+ vs HCO3 $$^{ - }$$ - /Na+, Ca2+/Na+ vs Mg2+/Na+, higher Na+ than Ca2+, and occurrence of CaCO3 concretions further supported geogenic processes that alter groundwater chemistry. The positive linear trend of TDS vs Cl $$^{ - }$$ - + NO3 $$^{ - }$$ - /HCO3 $$^{ - }$$ - and the relationship of TDS with TH showed anthropogenic input as the main factor, causing groundwater contamination. The WPI indicated two categories of water quality: moderately polluted water (WPI: 0.75–1.00) and highly polluted water (WPI: > 1.00) in 60% and 40% of groundwater samples, which were 81.49% and 18.51% of the study area, respectively. Hierarchical cluster analysis identified three clusters: Cluster I (pH, F $$^{ - }$$ - , Ca2+, K+, NO3 $$^{ - }$$ - , Na+, and SO42−), Cluster II (TH, Mg2+, Cl $$^{ - }$$ - , and HCO3 $$^{ - }$$ - ), and Cluster III (TDS) support WPI. Following WQI, 75% and 25% of groundwater samples fell under poor groundwater quality type (WQI: 100–200) and very poor groundwater quality type (> 200), respectively, especially due to the increased concentrations of Mg2+, Na+, K+, HCO32−, Cl $$^{ - }$$ - , NO3 $$^{ - }$$ - , and F $$^{ - }$$ - ions, thereby increasing salinity (TDS) and hardness (TH) in groundwater. Spatially, they covered 85.84% and 14.06% of the study area. The quality of this groundwater is not suitable for drinking purposes. Therefore, the present study suggests preventive measures (safe drinking water supply, desalinization, defluoridation, denitrification, calcium food, and rainwater harvesting) to protect human health.