The Killi River, an important tributary of the Karamana River, flows through the densely populated city of Thiruvananthapuram. Over the past few years, rapid urbanisation, population growth, and unplanned waste disposal have significantly degraded the quality of both surface and groundwater resources. This study attempts to assess the groundwater quality of the Killi River basin. Water samples were collected from twenty-nine open dug wells in February 2024 and subjected to physicochemical analysis following standard methods. The analysis results show that, at many locations, pH values fall below or exceed the permissible limits set by BIS (2012) and WHO (2011) standards. EC and TDS values are within the permissible limits. Elevated phosphate concentrations in many samples indicate anthropogenic pollution from sewage discharge, detergents, and agricultural runoff. Nitrite concentrations in all groundwater samples exceed permissible limits, suggesting significant contamination of the groundwater system. Groundwater facies is mainly Ca–Cl type, with some samples showing a tendency towards a mixed Ca–Mg–Cl water type. This suggests that alkaline earth metals dominate over alkali metals, and strong acidic anions exceed weak acidic anions. This reflects the influence of rock–water interaction, along with potential anthropogenic inputs, on groundwater chemistry. The groundwater chemistry of the study area is primarily controlled by water–rock interaction processes, as indicated by the Gibbs diagram. It can be concluded that the groundwater resources of the Killi river basin are suitable for domestic use, except for nitrite and phosphate. Hence, periodic monitoring is recommended to ensure long-term water quality and to detect any potential contamination.
Lal et al. (Sat,) studied this question.