Never thought of this idea for a basic supplemental water supply for the pond rather than trying to seal it perfectly. Since I live on a hill, and the pond is at the bottom of it, it would be reasonable to tap into a higher-elevation wet area at the opposite corner of the property from the pond. There would be a decent gamble of creating a "spring" and getting a flow without pumping. Not only that, my entire hill is made of glacial debris, so plenty of stones and clay rather than solid rock.
I will be following this thread to see what it ultimately costs to put one in. If you don't have to pump vs. pumping a vertical well, it would be far cheaper in the long run. Having a flow of cold water would also make trout possible, which would be a heck of a lot of fun.
