As you pull out Aunt Darcy’s book, you notice a paper that is folded up in between it and another book. You unfold it and see what appears to be a hand drawn timeline, with a circle around part of it:
Turning to page 12 of the book, you to see this figure:
The text explains that water stored underground still flows, albeit sometimes at very slow speeds. The amount of time it takes for water to enter and leave the ground varies substantially. In the uppermost aquifer, the path water follows through the ground is shorter and groundwater may travel through the aquifer in days or years. Deeper water is much older, at times as old as centuries or millennia. Water pumped from those deep regions might take many lifetimes to be replaced.
You wonder why Aunt Darcy was drawing the timeline and whether this is about her well water or somewhere else.