We plan to dig a borewell in Tumkur area - 80 km from Bangalore in Karnataka.
Geologist has predicted that we may get water at 650 feet below ground level.
One borewell driller, says that he will drill 650 feet and will need only ~
150-200 feet pipe to install. He says, he will hit rock at that level, after
which he will only bore till 700feet, without inserting pipe. It will be a
submersible pump at 200 feet.

Will this suffice?

We are ready to invest a little bit more also, but then want a long lasting
bore. we have another bore dug around 2 years back in which also they had
installed only 180 feet pipe with submersible pump.  When enquired about
why can't slotted casing pipes be used, he says since rock is there at 200 feet,
there is no need to insert anymore and he does not do that type of work.

My question is: What if rock is there only for 100 feet further, after which
soil or sand is there? Won't the depth of the bore stop at the end of rock (i.e.
200 feet pipe+100 feet rock)? Geologist has said the water source is good only
at 650feet.

Can you throw some light on this.

Ponni K