Dilution in water lowers contaminant strength, potency, and effect. Because concentrated toxic spills may need more dilution than soil water can offer, contain and remove the contaminants before they enter the ground. Livestock Wastes and Water Quality Animal manure has organic matter, plant nutrients, salts, and pathogenic microorganisms that can reduce water quality. Organic matter in rainfall or snowmelt runoff breaks down in streams and ponds by biochemical reactions. Those reactions can use enough dissolved oxygen to cause a fish kill.
Organic matter is filtered from water at the surface or in the soil.
So, organic matter often reaches surface water, but groundwater is largely protected. Microorganisms abound in animal intestinal tracts. Although documented cases of human disease from livestock waste are rare, transmissible livestock diseases from pathogens do threaten humans. The soil-climate environment is hostile to such microorganisms. As is the case with organic matter, they are filtered by soil above groundwater.