Groundwater from the middle Banat region (Serbia) which is used as a drinking water supply for Zrenjanin town contains a high amount of natural organic matter and a high content of arsenic. In this study a pilot-scale system was used to investigate the influence of different ozone doses (0.4-0.9 mg O3/mg DOC) during a pre-ozonation process on NOM removal by coagulation. Ferric chloride coagulant was chosen at a dose of 100 g/cubic meter, as a traditional coagulant which can also help in arsenic removal. The obtained results indicate that an ozone dose of 0.4 mg O3/mg DOC has the best influence on structural changes of NOM. The coagulation process with ferric chloride as coagulant had a significant influence on the arsenic content of the water, with the measured values in the water after coagulation in all three investigated treatment trains being below 10 microgram/l, which is the standard MCL in Serbian legislation.

The stable isotope content of hydrogen (2H/1H), carbon (13C/12C), nitrogen (15N/14N), and oxygen (18O/16O) in surface water (the Sava river and channels) and groundwater (Ranney wells) were determined in Belgrade (Serbia) during July 2008. Detailed evaporation calculation has estimated that fraction of water loss to be between 10 and 20% in the channels using the local meteoric water line and the local evaporation line. Carbon-13 content in dissolved inorganic carbon is distinguished between surface water and groundwater indicating different evolution pathways of carbon. Based on carbon and nitrogen isotopic composition and C/N ratios, sources of inorganic carbon and of organic matter in analyzed waters are discussed.

In the paper is presented the microbiological quality of groundwater of drinking water supply Strand which is important water source for the city of Novi Sad (Serbia). The examinations were carried out using high and low nutritive media. The count of physiological groups, that are relevant from the aspect of organic pollution and phosphatase activity were also monitored. The results indicate potential organical pollution and need for protection of the water supply Strand.

Content of arsenic in groundwater form south Banat which are used for water supply of local population was determined. 228 wells were analyzed, and for arsenic determination was used atomic apsorption spectrometry - graphite furnace technique (Perkin Elmer Analyst 700). Arsenic is detected in concentrations over 10 microgram/l in several locations: Pancevo (water supply Filter Stanica, Gradska Suma, OB, and in part of water supply Sibnica), Kovin, Dubovac, Idvor, Veliki Gaj, Glogonj, Sefkerin and part of Sakule. The lowest concentrations of arsenic are detected in the territory of Deliblatska Pescara and municipalities of Vrsac and Bela Crkva.