First multi-isotope characterization of water in the water supply system of Ljubljana / 7.07.2022

Stable water isotopes can help improve the understanding of freshwater resources. They can be used to better evaluate and map pathways of the domestic water supply system, even its interaction with different water bodies.

In the last decades, the increase in the development of large urban areas can be observed. This also brings a lot of water security problems due to excessive pumping, overexploiting, and water quality deterioration of local water sources. New approaches are required to address the problems. These have to do with how the water supply system (WSS) is behaving in time and space and how the properties of water in the WSS change from source to the end-user. Our study is the first such investigation in Slovenia (only one similar on a global scale) and is part of the research coordinated project by the IAEA. It describes the urban water cycle within the WSS of Ljubljana. A sampling of WSS was performed at different points between the source and end-user (wells, joint exits from water pumping stations, reservoirs, water treatment locations, drinking fountains, taps, and wastewater systems). Using stable isotopes (δ2H, δ18O, and δ13CDIC) we observed that each well has its own unique isotope fingerprint. We also proved that these unique isotope fingerprints change with a significant statistical difference between sampling months and environmental temperature. Finally, based on δ13CDIC values, a distinction could be made between river/groundwater interactions within the WSS and between shallower and deeper wells and their distance from the river bank.

The details are presented in the article published in Water: “Multi-Isotope Characterization of Water in the Water Supply System of the City of Ljubljana, Slovenia” prepared by K. Nagode, T. Kanduč, B. Bračič-Železnik, B. Jamnik and P. Vreča, available at: and the database at: