## 1 Introduction  
The Andean Highlands roughly extend between latitudes \(11^{\circ}\) N and \(8^{\circ}\) S, are over 3000 m a.s.l., play an important role in regional freshwater supply, and are highly sensitive to climate change [1, 2, 3]. As in other high mountain areas, most ecosystem typologies are groundwater dependent [4, 2, 5, 6]. The combined influence of global driving forces and some anthropogenic activities (e.g., deforestation, overgrazing, soil degradation, and water overdevelopment) is altering river flow and aquifer recharge regimes [4, 5, 6, 7, 8], with negative consequences for human water supply and the preservation of dependent ecosystems [2; 5; 8]. Rivers and streams have traditionally been the main freshwater source to meet the water demand of downstream urban areas [4; 9; 10]. Increased demand in many densely populated Andean cities has driven water source diversification [2; 4; 6; 10]. This is the case in the Metropolitan District of Quito city (MDQ) in northern Ecuador, where groundwater from the Andean Highlands and surface water transferred from the Amazonian watershed supplement traditional surface water sources [8; 10]. A question arises of how is increasing groundwater extraction affecting reserves and dependent ecosystems? Applied groundwater research aimed at defining the aquifer functioning is yet incipient to answer this question accurately [11; 12]. The Ecuador Water Authority and Quito's Public Water Supply Company (EPMAPS) are not immune to this problem. EPMAPS is responsible for prospecting, developing, distributing, and managing potable water in the MDQ, and promotes groundwater research to improve general hydrogeological knowledge as a prerequisite for a sustainable water supply. Hydrogeological studies use geophysical prospecting surveys to define aquifer geometry and certain transient groundwater features. Such studies typically cover two observation scales associated with two aquifer typologies. EPMAPS has used near-surface electrical geophysical techniques, such as electrical resistivity tomography (ERT) and vertical electrical sounding (VES), to explore shallow aquifer geometry and transient groundwater features required for drilling pumping wells intended to supply scattered population nuclei. The water company has also supported other public agencies and academic institutions can apply electromagnetic geophysical techniques for near-surface (very low-frequency electromagnetic methods, VLF-EMs) and deep (low-frequency magnetotelluric sounding, MTS) explorations to deduce the structure of shallow and thick regional geological formations catalogued as the larger freshwater reservoirs in the MDQ. Near-surface seismic prospecting techniques, such as refraction microtremor (REMI), have also been used to explore shallow geotechnical features. Such geophysical prospecting techniques have proven useful in groundwater research in different hydrogeological environments [13; 14; 15; 16; 17; 18]. They are non-invasive, usually inexpensive to apply, and useful when geotechnical sounding data is sparse or unable to provide subsurface information required for detailed groundwater research over multiple observation scales [15; 16; 17]. However, most geophysical prospecting surveys of interest in groundwater research are unpublished. Therefore, these experiences must be compiled and may need to be reinterpreted for groundwater research purposes. Such information concerning the aquifer saturated thickness, piezometric level, and spatial distribution of pore-water conductivity is essential to assess the fraction of groundwater that can sustainably supplement the urban water demand in the MDQ. This paper examines the feasibility of compiled geophysical prospecting surveys in groundwater research in the MDQ, providing findings of interest to improve the hydrogeological conceptualization and identifying research gaps that can be bridged in the near future.