1. Guangdong Hydrogeology Battalion, Guangzhou 510510, China; 

 To investigate the current water quality of potable groundwater sources, this paper utilizes methods such as mathematical statistics, Piper diagrams, Gibbs diagrams, and environmental background value statistics to study the hydrochemical characteristics and formation mechanism of groundwater drinking sources in Zhongshan City and its surroundings. The results show that the groundwater in the study area is weakly acidic and low in minerali?zation, with Na + and HCO - 3 being the main ions. The hydrochemical type is predominantly HCO3 ??Na·Ca. The chemical composition of the water is influenced by the combined effects of atmospheric precipitation and rock weath? ering, with a strong cation exchange reaction. The main reasons for the decrease in groundwater pH value are the long?term abundance of acid rain, the poor buffering capacity of the soil and aquifer in the vadose zone against acid deposition, and the hydrolysis of alkaline earth metals, CO2 and carbonates.