Here's why:

* Permeable Rock: Permeable rock allows water to pass through it. Think of a sponge. While caves can form in permeable rock, the cave itself is not the permeable layer.

* Cave Formation: Caves typically form in *impermeable* rock, like limestone. Water dissolves the rock over time, creating the cave.

* Water in Caves: Water can be present in caves, but it's usually in the form of:

* Groundwater: Water seeping through the surrounding rock and filling the cave.

* Surface Water: Water flowing into the cave from the surface.

* Water Features: Underground rivers, lakes, or even waterfalls within the cave.

In summary: A cave is a void or opening in the earth, formed by the dissolution of rock, not a permeable layer containing water. The water present in caves is usually groundwater or surface water that has entered the cave system.