Due to the scarcity of surface water in many regions around the world and the rapid increase in the population, there has been sharp increase in the potable water demand. Groundwater is becoming an important source of drinking water supply. In this study, for the first time, the isotopic composition (δ18O or δD) of precipitation and the karstic water resources and also the carbon isotope composition (δ13CDIC) of springs in Qori Meydan Plain (QMP - northeastern of Iran) were investigated. In QMP with semi-arid climate, springs have a key role in meeting water needs. Stable isotopic composition (δ13CDIC, δ18O & δD) of water resources were employed to trace their origin(s). The δ18O composition of these water bodies range from –9.6‰ to −7.5 ‰VSMOW with corresponding variation in δD varies from −69.0‰ to – 53.6 ‰ VSMOW. The water samples were plotted close to Global Meteoric Water Line (GMWL) which means that local precipitation is the main factor in recharging the water resources. Samples more exposed to sunlight (Qorte spring and Atrak river) have least d-excess values. DOC values in water resources predominantly originate from plants and green algae. The δ13CDIC ratios of water samples vary from −10.0 ‰ to -4.1 ‰VPDB, which points that the main source of DIC in groundwater is limestone beds.

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