I like this comment. Check that no water is being used and go look at the meter. Maybe you could unscrew the screen on a sink in the barn and see if any stuff comes out. When they install new water lines in Florida they pressure the line and attach a pressure meter for 24 hours or so to text if there is a leak. You could do that fairly easily.

Also I live below the frost line by a few hours. Our water line could be on the surface of the ground. 6 feet is nuts.