Abstract: Spring water is an important source of drinking water for the residents in the Hongjiadu Basin of Guizhou. However, with the rapid increase in human activities, the quality of the spring water has continuously degraded over recent years. To investigate the sources and geochemical processes of contamination in the springs, 15 representative water samples were collected for analyses of the characteristics of hydrochemistry and isotope of dissolved inorganic carbon (DIC). The spring water samples are dominated by Ca²⁺, Mg²⁺, HCO₃^- and SO₄^2-. Sulfuric and nitric acid, together with carbonic acid, are involved in the weathering of carbonate rocks. Spring S01 and S09 are considered unsuitable as drinking water sources due to exceeding concentration limit ofNa⁺, Cl^-, K⁺and NO₃^- in the springs mainly originates from sewage, fertilizer (e.g. chemical fertilizer and manure); SO₄^2- originates from sulfide oxidation in coal seams, acid rain, and sewage. The characteristics ofδ¹³C_DICin the Hongjiadu Basin are thereby considered to be mainly impacted from soil CO₂and weathering of carbonate rocks. Meanwhile, the participation of sulfuric and nitric acid in carbonate rock weathering leads to positiveδ¹³C_DICvalues and increasing concentrations of SO₄^2- and NO₃^- in the spring water, whereas the degradation of anthropogenic organic matter, bacteria sulfate reduction and denitrification result in negativeδ¹³C_DICvalues. These factors caused theδ¹³C_DICvalues of the spring water from the study area to fall within the range of -17.72‰ to -8.74 ‰ with a average of -11.58‰. This study confirms that the isotope ofδ¹³C_DIC, combined with hydrochemical analyses, is useful to examine the carbon biogeochemical processes and trace the pollutants sources in groundwater in karst areas.