In this study the data of arsenic content in groundwater of the Republic of Dagestan are presented. Due to naturally occurring arsenic in the sediments the groundwaters, used by population for drinking, content high level of arsenic compound. The contamination level varied from 1 to 500 μg L−1 with an average arsenic concentration of 190 μg L−1. 90% of water samples are above the WHO standard of 10 μg L−1. The high arsenic concentrations found in the artesian water samples (15.8% above 10 μg L−1 and 84.2% above 50 μg L−1) indicate that more than 500 thousand of people consuming untreated groundwater might be at a considerable risk of chronic arsenic poisoning. The evaluation of cancer risks from oral exposure to As were found to be above the acceptable U.S.EPA and WHO cancer health risk range of 1 × 10−6 to 1 × 10−4.