The work focuses on reassessment of groundwater quality of the Lower Kotlin aquifer complex by radiation indicators. At the first stage of the research the area radio-hydrochemical sampling of the aquifer complex was carried out with determination of ²²²Rn content, as well as indicators of total α- and β-activity. At the second stage, underground water in a limited number of sampling points was identified for radioactive isotopes: ²¹¹Ro, ²¹⁰Rb, ²²⁶Ra, ²²⁸Ra, ²²²Rn. The radiation safety index was calculated. Directions for further research are proposed.