The genotoxicity assay of drinking water in regional centers of North Kazakhstan oblast is carried out by a cytogenetic ana-telophase method using barley root tips. It is shown that drinking water of North Kazakhstan oblast is able to cause cytogenetic damages. A direct correlation between genotoxic properties of drinking water and the rates of congenital abnormalities, malignant neoplasms (by one of the most common localization in the oblast – a stomach cancer), gastric and duodenal ulcers among the population are revealed.