Increasing water demand and reducing its contaminations are the main concerns and challenges for water resource managers and planner due to its limited sources and high value. This study aims to assess and understand the factors which threaten the quality of groundwater resources and to achieve this, samples were taken from 14 active wells in District 3 of the Municipality of Tehran. After categorizing the parameters to distinct measurable groups containing anions (SO4, Cl, NO2, NO3, HCO3, CO3), cations (Mg, Na, k) heavy metals (Ag, Pb, Cd) physical parameters (temperature, color and odor) chemical parameters (Total Dissolved Solid , Electrical conductivity, Total Suspended Solids and pH, the data were analyzed using SPSS (version 16) software. The results revealed that excessive amount of nitrate anion in Paidari and Naji station is related to the slope and sandy texture of the wells and also the surrounding area’s soil. Increased cation concentration was visible in Resalat well, which indicated the use of excessive amount of fertilizers containing sodium and also the clay soil texture. Cadmium was the only heavy metal with the concentrations of more than the standard amount. Domestic sewage and surface runoff and also regional geological structure, the lack of appropriate distance between water wells with sewage wells were among other reasons, causing underground water pollution.