& objectives: Heavy metals enter water sources in many ways and cause hazards such as poisoning and carcinogenesis in the living organisms. This study aimed to investigate the concentration of heavy metals (arsenic, mercury, and cadmium) in the Yamchi Reservoir Dam and Ardabil drinking water distribution network in high and low rainfall seasons in 2018. Methods: In this cross-sectional study, eleven sampling stations were selected. Heavy metals such as arsenic, cadmium, and mercury were

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... . Paired t-test, Kruskal-Wallis, and Pearson correlation coefficients were used to test the research hypotheses using SPSS 21 software. Results: The mean electrical conductivity, temperature, and pH were 759.18±1.31 µmoh/cm, 10.18±2 2.08 ᵒC, and 7.69±0.5, respectively. The mean of the above variables in the low rainfall season was 887.72±27.11 µmoh/cm, 19.90±1.04 °C, and 7.76±0.44, respectively and these values were at the national standard. The mean arsenic, mercury, and cadmium concentrations in the rainy season were 32.18±4.61, 59.94±8.75, and 21.28±6.03 μg/l, respectively. The mean of the above variables in the low season of precipitation were 976.37±205.90, 549.05±109.32, and 5.30±2.47 µg/l, respectively and these values were higher than the national standard. Conclusion: In conclusion, the location of sampling stations influences the determination of heavy metals (arsenic, mercury, cadmium) in Yamchi Reservoir Dam and Ardabil drinking water distribution network in high and low rainfall season. Temperature and electrical conductivity had a significant positive and significant effect on arsenic and mercury concentrations; but pH did not affect on the concentration of heavy metals (arsenic, mercury, cadmium) in Yamchi Reservoir Dam and drinking water distribution network in Ardabil city during high and low rainfall in 2018.