The Ljubljansko polje and Ljubljansko barje aquifer system are the two most important groundwater sources for the Slovenia capital Ljubljana and its surroundings. The groundwater is pumped from 4 wellfields on Ljubljansko polje and one wellfield on Ljubljansko barje. In the central water distribution system some settlements are supplied with water from a single water plant, while some receive water from two or more facilities, depending on the volume of consumed water and pressure conditions. In Ljubljana, the water is prepared in a local water supply system without any technical water preparation procedures and is only chlorinated occasionally. Public Water Utility JP VODOVOD KANALIZACIJA SNAGA Ljubljana (JP VOKA SNAGA) monitors the microbiological and chemical parameters of drinking water at all stages. In 2018 started a new IAEA Coordinated Project F33024 "Use of Isotope Techniques for the Evaluation of Water Sources for Domestic Supply in Urban Areas" in which researchers from 16 countries worldwide participate. The Specific Slovenian Research Objectives in CRP are to improve the assessment of most important freshwater resources for domestic supply using environment isotopes, to select significant environmental isotopes for future monitoring that will enable better understanding and interpretation of water interactions important for water managers of JP VOKA SNAGA to predict the availability and quality of freshwater resources for Ljubljana domestic water supply and to develop together with JP VOKA SNAGA and CRP project partners guidelines on integrating environmental isotopes to assist water managers in the planning, designing, and management of freshwater resources for domestic supply in urban environments. Based on the synthesis of the results from previous investigations in the area and the experiences of JP VOKA SNAGA, 97 sampling sites in the Ljubljana water supply system were selected. Sampling sites were selected according to the water supply area and according to the type of sampling sites. Selection according to the type of sampling site in the water supply system includes 6 different types: wells (VD; 44 samples), joint exits from water pumping station (ZV; 7), reservoirs (VH; 23), water treatment locations (PV; 2), drinking water fountains (PIT; 13) and water tap in public buildings (PJ). Additionally, 10 sampling sites were selected including water taps in 2 public and 8 private buildings (PP) which are not included in regular monitoring of JP VOKA SNAGA. Selection according to the water supply area includes 8 different areas: 4 main water fields: Kleče (A), Hrastje (B), Brest (C), Jarški prod (D), Šentvid (E), and 4 areas where the water is mixed from two or three different supply areas: Hrastje/Jarški prod (F), Kleče/Brest (G), Kleče/Hrastje/Jarški prod (H) and Kleče/Hrastje/Brest (I2). Finally, sampling sites on River Sava (R: Brod, Črnuče, and Šentjakob) and at the outflow from wastewater treatment plant (CČN) were also selected. Sampling was performed between 06.09.2018 and 29.11.2018. This database is summarized results of in-situ measurements (water temperature and electrical conductivity) and laboratory analysis (pH, total alkalinity, the concentration of total arsenic in water, isotope composition of oxygen, hydrogen and carbon in dissolved inorganic carbon).
