Need suggestions on best way to detect underground water resource


I know this particular question has been asked many times in the same forum. But the curosity and level of frustration due to a failed attempt is making me ask it yet again. Few days ago I hired a Govt retired geologist for finding out points for borewell that could yeild good amount of water for my farm located around 40 Kms from Bangalore. He used an instrument that closely resembled a Brunton compass (may be it is the same instrument). He walked around the farm and was monitoring the needle deflections. He suggested a point which he said has good source of groundwater and suggested that we drill a bore around 650-700 feet deep. He said I would get around 190 GPM (2.5") yeld. When the drilling started, we got water of around 80 GPM (1.5 ") at a depth of around 450 Feet. With hope for higher volume of water (as suggested by the geogologist), the drilling was continued upto 960 Feet, but there was no improvement in the volume of water.

This has led to disappointment and waste of money on drilling. 

Can anyone shed some light on the techinque used by the geologist? How reliable is the method and the chances of success. Also a comparison on other methods like soli resistivity and PMR will really help understand this better.

I would also appreciate any pointers to good hydrogeological firm who specializes in underwater exploration using advanced techiniques.

Thanks and Regards

Satish Rajanna