## 4 Conclusions  
The spatiotemporal multivariate evaluation of drinking water from different supply zones located in Sibiu County, Romania, provides a comprehensive view and allows observations on the correlations and variability of quality parameters in relationship with the water source, location, and period of sampling. The validity of the hereby applied statistical techniques was confirmed by results.  
For all radioactivity parameters, the water source was the best predictor in the fitted model of GLM with gamma distribution (for gross alpha activity and gross beta activity, respectively), and GLMM with gamma error distribution (for Rn-22 content). According to  
Figure 9: Biplot of the co-inertia analysis between radioactivity (gross alpha and gross beta activities) and physical-chemical parameters.  
the RDA results, water radioactivity increased from surface to deep and subsurface sources. The co-inertia analysis between radioactivity and physical-chemical parameters showed a positive correlation of the gross alpha activity with turbidity and residual chlorine, while the gross beta activity was positively correlated with conductivity, Cd, and Mn. Water radioactivity in Sibiu County is low, compared to other investigated areas, but further studies are required for examining groundwater sources used by small communities.  
Certain chemical contaminants such as ammonia and Fe may be of concern, especially ammonia in rural localities due to agricultural practices and the pastoral character of the area. The variability of the physical-chemical parameters and 5-year trend is explained (RDA) by the water source, month of sampling, and locality. Results are significant for turbidity and Fe level in surface water (with highest values in August), and for conductivity and nitrates level in ground water (with high values in January). High pH and concentrations of residual chlorine and ammonia were characteristic for March. This monthly variation of contaminants may be useful for more efficient operational management and population awareness, with particular interest for the rural localities of Sadu and Seica-Mare. The present model highlights that the water source from the mountain resort Palitinis was the best drinking water in the studied interval in terms of quality, according to the Romanian, European, and WHO requirements.  
Our model illustrates a potential approach to water monitoring programs. It may be further optimized by using a more comprehensive dataset from a longer survey period, and also a larger number of predictors describing the environment, which would increase its applicability for local authorities to draw appropriate water quality management measures.  
Conceptualization, C.I.T., S.O., M.S., A.M.B. and M.D.C.; methodology, C.I.T. and A.M.B.; investigation, C.I.T.; resources, S.O. and A.M.B.; data curation, S.O., A.M.B. and M.S.; writing--original draft preparation, M.S., C.I.T. and A.M.B.; writing--review and editing, M.S., A.M.B., S.O. and M.D.C.; supervision, S.O.; funding acquisition, S.O. All authors have read and agreed to the published version of the manuscript.  
The project was financed by the Lucian Blaga University of Sibiu (Knowledge Transfer Center) and Hasso Plattner Foundation research grants LBUS-HPI-ERG-2023-04.  
Not applicable.  
All data are contained within the article.  
We wish to acknowledge the help provided by [PERSON] in drawing up the map of sample collection points and water sources.  
The authors declare no conflict of interest.