There is no easy way to do this, we had special equipment that would listen for underground streams so we would not drill or blast into one. Some are very hot and move a lot of water .
Another way they would do is use a listening device like a Doctor would use to hear if anything was there.
If you think it is a dry hole then you might have to drill a pilot hole into the wall to see . You can use a star drill and one other man to do this. Some would use a laser thermal gun to see if there was a big temp change in a small area !
But other than that you may need a detector that was made to look for those. You might be able to rent some of this equipment to see if it will help you find out .
But there is no easy way that I have seen or used , now someone on here might know of something that I do not .
Good luck !