Antimony (Sb) is a major environmental pollutant that is widely present in nature and possesses toxicity and potential carcinogenicity. The mining of antimony ore can affect the quality of the water environment and the safety of drinking water for residents in the area. Taking the Gaolinggou antimony mining area in the Danjiangkou water source for the Middle Route of South-to-North Water Diversion Project (MRSNWDP) in China as the research object, systematic hydrochemical samples and hydrogen and oxygen isotope samples were collected for comprehensive hydrogeochemical analysis. The results show that: (1) The pH range of surface water in the study area is 3.09-8.30, with a mean of 7.21, indicating an overall neutral condition, while some local areas are acidic. The range of TH is 243.00-439.00 mg/L, with a mean of 314.69 mg/L. The TDS ranges from 262.00 to 598.00 mg/L, averaging at 384.38 mg/L. The dominant cations are Ca²⁺ and Mg²⁺, while the dominant anions are HCO₃^- and SO₄^2-. The hydrochemical types vary frequently in space, including HCO₃·SO₄-Ca·Mg, SO₄·HCO₃-Ca·Mg, HCO₃-Ca·Mg, and SO₄-Ca·Mg. For groundwater, the mean pH is 7.52, with TH and TDS ranging from 269.00-542.00 mg/L and 291.00-652.00 mg/L, respectively, averaging at 426.67 mg/L and 504.67 mg/L, both slightly higher than those of surface water. The dominant cations and anions are Ca²⁺ and HCO₃^-, respectively, with hydrochemical types mainly HCO₃-Ca·Mg and HCO₃·SO₄-Ca·Mg. The mine water has a pH value of 8.03, indicating a weakly alkaline condition with the highest TDS content. It is rich in SO₄^2-, Ca²⁺, and Mg²⁺, and the hydrochemical type is SO₄·HCO₃-Ca·Mg. (2) The hydrochemical characteristics in the study area are primarily controlled by rock weathering, with carbonate and silicate weathering and dissolution as the main processes. Positive cation exchange occurs in the water bodies. Surface water is significantly affected by mining activities, while groundwater is influenced by a combination of agricultural activities, domestic sewage, and mining activities. (3) In addition to atmospheric precipitation and dissolution of salt rocks, the excess Na⁺ in the water bodies mainly originates from the dissolution of sodium-bearing silicates and the contribution of cation exchange processes. Ca²⁺ and Mg²⁺ mainly originate from the weathering of carbonate rocks dominated by calcite and the dissolution of gypsum. Carbonic acid and sulfuric acid both participate in the weathering and dissolution of carbonate rocks. So₄^2- and Cl^- are significantly influenced by mining activities. The antimony in surface water is primarily influenced by the mining of antimony ore, with the average concentration of antimony in the mining area being 6.4 times that of the mainstream of the Luohe River. Meanwhile, the antimony in groundwater mainly originates from the lateral recharge of surface water. The results can provide a reference for the water resource security assurance and rational development and utilization of the MRSNWDP.