This simple procedure not only prevents pollution of the water system but also is a way to conserve a major resource. Highly dangerous chemicals used in agriculture as weed killers and insecticides can also pollute the water system. As much as 600 pounds of insecticides are sprayed each year on each acre of agricultural land, and consequently streams contain about 2 pounds of insecticide per million gallons of water. In addition, the effects of these insecticides on humans and fish have largely been ignored. These pollutants have a number of effects on animals, humans and aquatic fauna.
Domestic animals are also a source of water pollution.
The washing of barns and other buildings, and water flowing from manure piles, produces a waste that enters the groundwater system as well as surface streams. Coal seams, primarily bituminous, have sulfur deposits. When these iron sulfide deposits come in contact with water, a weak sulfuric acid results. The acid drainage from both surface and underground mines has acidified thousands of miles of streams. The acid mine drainage has affected the ecology of the streams as well as the use of the water for many industrial purposes.