From agriculture. In the process of cultivation is often the use of fertilizer and chemical defense. Most examples lack the caution. Make the chemicals spread to the water supply.
Runoff from agriculture In the process, often with the use of fertilizers and crop protection chemicals. Most used indiscriminately. Thus spreading the chemicals entering the water.
Waste water from agriculture. In the process of cultivation is often the use of fertilizers and chemical protection. Mainly used as a lack of caution. The chemical spread to the water.