Maybe this is a naïve question, but what lies beneath groundwater?
I'm not talking about cases of perched water tables, where groundwater sits on top of an impermeable aquitard. In such cases it's obvious what lies beneath the groundwater (an aquitard).
But in general, what is beneath groundwater? The uppermost extent of groundwater is referred to as the water table. Is there an equivalent lowermost extent?
Does groundwater extend into the mantle, or is it confined to the crust?
Every diagram I've seen that explains groundwater is cut off at the bottom and doesn't show what's underneath and doesn't show groundwater in a larger context (i.e. its deepest extent)