system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does water poured onto already moist potting soil soak in faster than water poured onto completely dry potting soil?
gpt
When the soil dries completely there are hydrophobic residues on the surface that prevent the water from being absorbed until the surface tension is broken.

ELI5-er:
When the soil dries completely, waxes and oils in the soil protect the surface.

Kind of like the way it is hard to wet a new towel.

Source: asked this exact question in hydrology class once.