地下水都藏在地下大河里吗？把岩土想成有空隙的材料

Generally, water underground is more like water in a sponge. It occupies the spaces between soil and rock particles.

Even though there are some caverns, lava and ice tubes, and horizontal springs that can carry water, the vast majority of underground water occupies the spaces between rocks and subsurface material.

Water moving below ground depends on the permeability (how easy or difficult it is for water to move) and on the porosity (the amount of open space in the material) of the subsurface rock.

孔隙度描述空隙多少，渗透性描述水通过材料的难易，二者不是同一指标。

If the water flows through the rocks easily enough to be pumped and used by people then the formation is called an aquifer.

含水层还需有足够透水性，不是有孔隙就必然能抽取供水。

At a certain depth below the land surface, the spaces between the soil and rock particles are totally filled with water.

只描述地下水位以下孔隙充满水的情形，不说明所有岩土都易于透水。

Gravity and pressure move water downward and sideways underground through spaces between rocks. Eventually it emerges back to the land surface, into rivers, and into the oceans to keep the water cycle going.