## 5 Conclusions  
The hydrogeophysical survey technology successfully developed and demonstrated at four contrasting sites in Malawi was designed to be low cost, easy to use, efficient and accessible to developing countries. The technology uses multiple vertical electrical soundings (VESs) to generate a true 2-D resistivity image of the geological subsurface complexity that successfully distinguishes a wide range of (hydro)geological features having an imaging performance that appears comparable to that of the much more expensive 2-D surface ERT. The technology is vastly superior to 1-D hydrogeophysical reconnaissance tools currently employed in Malawi to aid borehole siting. Its adoption could make valuable use of existing VES equipment and knowhow already present, and overcome ERT affordability issues. There is, hence, significant opportunity for technology deployment in Malawi. This is under discussion nationally. Widespread application would allow much improved targeting of local aquifer resource, more optimal and sustainable siting of boreholes and hence greater resilience of Malawi's rural water-supply infrastructure, thereby underpinning attainment of SDG 6 targets. Technology application to the wider developing world is perceived useful, especially where current hydrogeophysical reconnaissance methods are lacking and (hydro)geological complexities are more probable.  
The following are available online at [[https://www.mdpi.com/2076-3417/11/3/1162/s1](https://www.mdpi.com/2076-3417/11/3/1162/s1)]([https://www.mdpi.com/2076-3417/11/3/1162/s1](https://www.mdpi.com/2076-3417/11/3/1162/s1)). Figure S1: Geological map of Malawi. Box S1: Practical construction details of the VES cable system used. Table S1: Sequence of electrode combinations for the acquisition of resistivity measurements. Figure S2: Series of fully collinear soundings for 2-D surveys. Figure S3: General sequence of acquisition and measurement parameter settings for surveys. Table S2: Details of input files for resistivity inversion freeware R. Figure S4: Example quadrilateral mesh used for resistivity inversions. Figure S5: Muzongo survey: preliminary interpreter subsurface resistivity cross-section AB (final interpretation is made in Figure 9). Figure S6: Sedimentary environments interpreted from the Chiluwe outcrop analyses. The geophysical survey data presented are provided in the file: Geophysical survey -- field results.  
Conceptualization, R.L., R.M.K., M.O.R. and P.S.; methodology, R.L., P.S. and R.M.K.; software, R.L.; validation, R.L., and M.O.R.; formal analysis, R.L.; investigation, R.L. and G.J.W.; resources, P.S., G.J.W. and R.M.K.; data curation, R.L.; writing--original draft preparation, R.L., and M.O.R.; writing--review and editing, M.O.R., R.M.K., P.S., R.L. and G.J.W.; visualization, R.L. and M.O.R.; supervision, R.M.K. and P.S.; project administration, R.M.K.; funding acquisition, R.M.K. All authors have read and agreed to the published version of the manuscript.  
This research was funded by research by the Scottish Government, under the Scottish Government Climate Justice Fund Water Futures Programme (CJF) research grant HN-CJF-03, awarded to the University of Strathclyde ([PERSON]).  
Not applicable.  
The geophysical survey data presented in this study are provided in the Supplementary Materials.  
We acknowledge the support of [PERSON], [PERSON] and [PERSON], all formerly of the University of Strathclyde, in the planning and execution of the geophysical survey fieldwork in Malawi. [PERSON] of University of Lancaster is thanked for the provision of the R2 software.  
The authors declare no conflict of interest.