It must be a spring. We had one under our old house and when we lost power during heavy rain it would just rise up and flood the basement.
That’s what we thought too. There are steps next to a spot that looks like an “indoor” well. They left them when they built the back of the house as a breakfast nook.
The breakfast nook was a porch. We think the farmer had a covered porch for his wife to get water in the cellar so she didn't have to brave the elements. And the cows. lol