Carbon isotope analyses can be used for knowledge and practical purpose. They can be used to assess the genesis of carbon in geochemical environment, and may also be used to indicate groundwater contamination by carbon-containing compounds. Based on this method it is possible to delineate contamination area by the activity of the landfill site. The aim of the paper is to indicate the possibilities of using carbon isotope composition for interpretation surface water and groundwater in terms of natural and anthropogenic factors influencing their quality. This method can be applied universally in water research, because carbon sources are different in isotopic composition.