Perhaps I can give you a few ideas to consider.  Realistically, you may have only a few things available and have only very specific needs for your purposes.  Some of these may be more attributes to layers than actual layers.  Geology/substrate materials and maps if available including faults, fractures, geologic layers.  By location, depth to various members such as aquifer confining layer(s), water quality components or attributes of each aquifer, extent of each aquifer, range of hydrologic conductivity within aquifer or layer as an attribute, hydric soils or depth to layer with hydric characteristics - common zone of saturation, measured range in water table (head), location of water wells, rainfall and stream gauges, locations of geologic or soil sampling, or well or other groundwater studies with data referenced or connected to the sites.  You may need both plan maps of surface features and cross section maps.  If there is a lot of wells being pumped, you may want to have contour maps of water table surface with cones of depression mapped.

I suggest 2 pubblications that speak about two methods for groundwater vulnerability  (SINTACS and DRASTIC). Specifically  these articles give you informations about layers for map groundwater vulnerability.

Cusimano G.; De Maio M.; Gatto L.; Hauser S.; Pisciotta A. (2004) Application of SINTACS method to the aquifers of the Piana di Palermo(SICILY, ITALY), In: GEOFISICA INTERNACIONAL Elsevier, pp 10, ISSN: 0016-7169

Amit Ghosh, Ashwani Kumar Tiwari , Santosh Das (2015). A GIS based DRASTIC model for assessing groundwater vulnerability of Katri Watershed, Dhanbad, India. In: Model. Earth Syst. Environ. (2015) 1:11. DOI 10.1007/s40808-015-0009-2

In my opinion the area where groundwater potential zone mapping is to be considered, includes

 1 geology/soil cover,

2  lineaments,   

3 nature and geometry of aquifer,

4 rainfall distribution,  

5 drainage density,

6  groundwater level fluctuation,

7 average depth of wells,

8 storativity and transmissivity values,

10 DEM and Slope , and

11. Land use Land cover map of the area.

The weighed overlay analysis in GIS as well as AHP technique will be useful to obtain the potential zones.

You may see this article

http://link.springer.com/article/10.1007/s12517-012-0779-z