Adi Ganga, an open canal in Kolkata, constitutes a dump to a large part of the urban wastes produced. The constant and uncontrolled disposal of the wastes contributes to the degradation of water quality of Adi Ganga, which in turn might have adverse effect on groundwater in the adjoining areas. Surface water (SW) and groundwater (GW) collected from six locations along Adi Ganga were analyzed to understand the extent of degradation caused due to SW pollution. Among the important water quality parameters and heavy metal analysis - dissolved oxygen, turbidity, total hardness, alkalinity, biological oxygen demand, oil and grease and zinc of both SW and GW were found to be much greater than their respective permissible limits (WHO, 2004). Both the SW and GW samples depicted phosphate and bicarbonate beyond their recommended values whereas; cations were well within the limit. Hydrochemical analysis through Piper, Stiff, Stabler, Schoeller-Berkaloff and Wilcox diagrams indicate that the water is dominated by calcic and magnesian facies with chlorinated and bicarbonate water types with higher alkalinity. Average water quality index of 33.7 and 52.4 for SW and GW indicate that these are severely and marginally threatened, respectively. Cluster analysis and Pearson's correlation studies show similar trend for both SW and GW indicating role of SW pollution in quality degradation of GW. The SW quality parameters found beyond permissible limits are mainly contributed anthropogenically therefore, immediate stoppage of further pollution of SW is imperative to stop degradation of GW quality, a regular and reliable source of drinking water.