Improving soil structure results in more water infiltration and less runoff, giving the ground an improved ability to absorb water during intense rain events.
This natural regulation of the hydrological cycle reduces the economic and environmental impact of floods and droughts. It also contributes to a healthy water table, feeding springs, streams, and lakes. Healthy soil acts as somewhat of a filtration system that incubates decomposing organics wastes. Properly managed soil systems can not only store carbon, but can also degrade and sequester other gases and compounds that could pollute the water or air in a region.
Beneficial agricultural practices help stave off soil degradation by not tilling, planting cover crops, and using managed integration of livestock to reduce inputs.
The National Research Council lists these points about the relationship between soil degradation and water quality:
Soil degradation causes both direct and indirect reductions in water quality.
Even though fertilizer runoff can occur agnostic of soil erosion, soil degradation from erosion leads directly to water quality issues.
Soil degradation impairs the capacity of soil to regulate water flow through watersheds.