Daily Fluctuations in the Isotope and Elemental Composition of Tap Water in Ljubljana, Slovenia

The isotope and elemental composition of tap water reflects its multiple distinct inputs and provides a link between infrastructure and the environment over a range of scales. For example, on a local scale, they can be helpful in understanding the geological, hydrogeological, and hydrological conditions and monitor the proper functioning of the water supply system (WSS). However, despite this, studies examining the urban water system remain limited. This study sought to address this knowledge gap by performing a 24 h multiparameter analysis of tap water extracted from a region where the mixing of groundwater between two recharge areas occurs. This work included measurements of temperature and electrical conductivity, as well as pH, delta H-2, delta O-18, d, delta C-13(DIC), and Sr-87/Sr-86 ratios and major and trace elements at hourly intervals over a 24 h period. Although the data show only slight variations in the measured parameters, four groups were distinguishable using visual grouping, and multivariate analysis (Spearman correlation coefficient analysis, hierarchical cluster analysis, and principal components analysis). Finally, changes in the mixing ratios of the two sources were estimated using a linear mixing model. The results confirm that the relative contribution from each source varied considerably over 24 h.

Automated summary

The isotope and elemental composition of tap water provides a link between infrastructure and environment, helping to understand geological and hydrological conditions and monitor the functioning of the water supply system. Despite limited studies on urban water systems, multiparameter analysis can address this knowledge gap by identifying distinct groups and estimating changes in mixing ratios over time.