Therefore, the water sources are not monitored for maximum contaminant levels as public water systems are. Because agricultural run-off is a diffuse source of pollution, it is hard to control. Non-point source is most simply defined in contrast to point source pollution,which comes from a specific place such as a pipe or smokestack. Contaminant concentrations arising from industrial or other point sources can easily be measured at the 'end of the pipe'. Non-point source pollution is difficult to assess because the source is spread over a large area, as in agricultural or mining regions.
Pesticides are a threat to health due to their inherent toxicity.
There are many types of pesticides and exposure depends upon many factors. Nitrates are the major constituent of fertilizer which poses a health threat, particularly in infants under 6 months of age. Excessive amounts of Phosphate can degrade water quality. Nitrates and phosphates cause eutrophication of surface waters such as lakes, streams and rivers. Eutrophication is a natural process of enrichment of a water body by the addition of plant nutrients.