* Structure: Solid rock is made of tightly packed minerals, leaving very little space for water molecules to move through.

* Pores: While some rocks may have small pores, these are often too small or filled with other materials to allow water to flow easily.

* Density: The dense structure of rock prevents water from seeping through.

Exceptions:

* Fractures and Cracks: Water can pass through rock if it has fractures, cracks, or other openings.

* Porous Rocks: Some rocks, like sandstone, are more porous and allow water to pass through them.

In Summary: Solid, intact rock acts as a barrier to water flow due to its dense, tightly packed structure.