Dear maahey: I didn't know Bermuda was a coral atoll.
If the ring was a complete circle, that would keep salt
water out if there were enough rain. I know of wells close
to shore on Cape Cod. However, it may well be that Bermuda
has lowered fresh water table enough to create a relative
water shortage. From what I have read, rainwater cisterns
are needed there. But if the island is an atoll, no dowser
would be needed.
Again, I shake my head at the idiocy of pointing dowsing
rod at a map.(Or anywhere else!)