The deposit groundwater in the Kurortnij district can be characterized by some hydrochemical special features. First of all there is contribution of Fe, Mn, Rn, etc. The composition of groundwater depends on different conditions: pH, Eh, organics, etc. Solving the problem of groundwater hydrochemical changes there is a need to continue the investigation of groundwater on the territory of St.Petersburg. It allows to improve the organization of the central water supply system.