Balcova Geothermal Field hosts the largest geothermal district heating system of Turkey and a number of shallow groundwater wells that are used for irrigation of the agricultural activities. The present study aims to assess the influence of geothermalfluid on groundwater by determining the hydrogeochemical properties of the water resources. A sampling program was conducted for 10 months and samples were collected from geothermal and groundwater wells including re-injected fluid. Trace and major elements, and the types of waters were determined. The results of groundwater analysis showed that the concentrations of some toxic species, such as arsenic, boron, and fluoride, eXceeded the limits of drinking water standards set by TSE, EPA, and WHO.