The major factors governing the formation of the chemical and isotopic compositions of surface water in open water bodies (ponds) in the Bodrak River basin have been studied by hydrochemical and isotopic methods. Special attention was paid to studying rainwater, because the chemical and isotopic compositions of atmosphere precipitation, as well as its volume are of great importance in studying the geochemical features and water budget of surface water bodies. The study is based on field data collected during long-term observations: the hydrochemical monitoring was carried out in 2003–2007, and the isotope samples (2Н and 18О) were taken from 2012 to 2018. The analysis of data shows that the chemical and isotopic composition of surface water in the area under study depends on the volume of atmospheric precipitation and flood water, weather conditions, and the geological–hydrogeological environment, which determines groundwater inflow, as well as anthropogenic factors.