Best to consult geologist or geological agency, who will be familiar with landforms, geology testing and well logs for each physiographic area, as well as know about aquifer information, perhaps even plots or GIS coverages appropriate for this type study.  A groundwater hydrologist may also be able to contribute to the specifics of your questions and perhaps update you on available data or tools, studies, etc. within or similar to your area of interest.  

There are different methods available for groundwater exploration such as hydrogeological; geomorphological; geophysical; tracer technique and of course remote sensing. GIS is only a mapping soft ware, wherein you can prepare the groundwater potential maps or any other output using GIS software by assigning information deciphered from the earlier mentioned techniques or methods. Generally remote sensing technique is used in regional mapping of groundwater potential zones by extracting or deciphering information on geology; geomorphology; landuse; soils; etc. Further to this field investigations will be conducted through hydrogeological and geophysical surveys to pin point well locations. Thus application of remote sensing technique in groundwater development / exploration is a first step, whereby one can reduce the field investigation, but one can not avoid field investigations or remote sensing is not a replacement to field investigations such as hydrogeological and geophysical.

Very well explained by respected William F. Hansen and N B Narasimha Prasad. You can look for published reports such as fence diagram, penal diagram so that it will make your work easier and faster.  

Is not posible yet. You need use other methods like geophysical or exploration wiht some direct method. 

Vertical Electrical sounding is one of the widely used techniques. 

Depending on probable depth of the acquifer, a number of geophysical methods can be employed. Like Raju already pointed out, point soundings for vertical electrical variation of the earth can be used. For a complete lateral image, you might want to employ the electrical resistivity tomography (ERT). A 48-channel unit at 10m separation of electrodes should give you ~95m mid-spread depth resolution.

Dear Dhakal,

It is not possible to locate aquifer horizons from GIS. GIS depends on existing geologic, geomorphologic and geophysical information. N.B.N. Prasad, has given an elaborate explanation on the use of GIS, which can enable you isolate groundwater potential areas. Basically, the electrical resistivity methods (VES and ERT) are suited for aquifer delineation and has enormous advantages.

Regards

Ebong