Steep slope and permeability would be the conditions on the surface of the Earth, which will permit for the greatest concentration of water to seep into the ground.
A gentle slope would signify that the water will run down gradually, and if the slope is much gentle, that is, if the ground is too much flat, then the water would stay on the surface and would give rise to form of water bodies like a lake.
Also, permeability that is the quality or state of a substance, which makes it permit the gases or liquids to go through it. Thus, if the surface of the soil is more permeable, it will allow more water to pass through it.