Your method of using an underground water source is great. I had the same thought on a lake house I looked at. The water temperature was about 55 to 65 degrees year round since the water came off the bottom of a damn. Just using that water to keep the house air in that temperature range to start before additional heating or cooling is a major energy saving.
Well as I said in another post, the water source was more luck than good planning but I’ll take it.
If had a lake house, I’d be looking at something like that as well. One thing to keep in mind is that if the water has to travel some distance, there are obviously pumping costs but in addition to that, if the distance is significant to the house, there will be thermal losses as well... it might start off at 55 to 65 degrees but will be where it is used? That’s the important question.