## 6 Conclusions  
The favorable climate in the Mediterranean coastal area has potentiated an increasing urbanization and occupation of peri-urban areas for profitable irrigation agriculture. The new land uses and water demands have evidenced the controversy of having a scarce conventional water resource, while the intensive water use generates a difficult-to-manage non-conventional water resource that may complement the conventional one. In the context of global change and growing water demands, the small marginal aquifers in urban and peri-urban areas may play a role in complementing the urban allotment for specific uses. The smart cities in the near future will consider new paradigms for sustainability such as \"water recycling and reusing\".  
Adra town in southern Spain was the case study chosen to show this problematic and introduce a feasible methodology to conceptualize the NSUS aquifer functioning and provide a tentative magnitude of the groundwater resource contributed to the SFUS. For this, findings from the geological, geophysical, hydrological, and hydrogeological surveys were combined to create a 1:5000 scale hydrogeological map and cross-sections, which are basic tools to design a proper urban water planning. The MASW and GPR geophysical techniques were especially useful for aquifer geometry definition. The NSUS average groundwater discharge was evaluated around 0.28 Mm\({}^{3}\) year\({}^{-1}\). Among other uses, this resource may guarantee a permanent water supply to watering public gardens and urban cleaning, which is currently around 0.11 Mm\({}^{3}\) year\({}^{-1}\) and will increase due to new urbanized areas, thus alleviating the pressure on the ARDGB.  
This paper seeks to offer a feasible methodology for groundwater research in medium-size urban areas having steep topography, low-permeability bedrock underlying shallow urban aquifers, and peri-urban areas influencing the urban hydrology. The authors found that the introduced basic formulation for groundwater discharge enables for a tentative evaluation of this resource at most. For this reason, solving of the discussed hydrogeological gaps and designating of suitable sites for a sustainable groundwater exploitation regime will be subjects of future research.  
Conceptualization, F.J.A.; methodology, F.J.A., P.M.-P., M.C.P., and M.N.; formal analysis, P.M.-P., M.C.P., J.P.-C., and M.N.; data curation, M.C.P. and J.P.-C.; writing--original draft preparation, F.J.A.; writing--review and editing, F.J.A., P.M.-P., M.C.P., M.N., and F.D.; project administration, F.J.A.; funding acquisition, M.N. and F.D. All authors have read and agreed to the published version of the manuscript.  
This research was partly supported by the Spanish Research Projects CGL2016-78075-P and CGL2007-66745-C02-02/BTE, and the Andalusian Research Projects IE17_5560_EEZA and P06-RNM-01732, all including European Regional Development Funds.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors are grateful for the information on the urban and irrigation water supply systems provided by the Water Authority of Adra town and local Water Users Associations, respectively. [PERSON] from University of Porto is also acknowledged for providing GPR equipment and software. The valuable comments and suggestions by two anonymous referees are greatly appreciated.  
The authors declare no conflict of interest.