Sewage: Untreated or inadequately treated municipal sewage is a major source of groundwater and surface water pollution in the developing countries. The organic material that is discharged with municipal waste into the watercourses uses substantial oxygen for biological degradation thereby upsetting the ecological balance of rivers and lakes. Sewage also carries microbial pathogens that are the cause of the spread of disease. Nutrients: Domestic waste water, agricultural run-off, and industrial effluents contain phosphorus and nitrogen, fertilizer run-off, manure from livestock operations, which increase the level of nutrients in water bodies and can cause Eutrophication in the lakes and rivers and continue on to the coastal areas. The nitrates come mainly from the fertilizer that is added to the fields. Excessive use of fertilizers because nitrate contamination of groundwater, with the result that nitrate levels in drinking water is far above the safety levels recommended.
Good agricultural practices can help in reducing the amount of nitrates in the soil and thereby lower its content in the water. Synthetic organics: Many of the 100 000 synthetic compounds in use today are found in the aquatic environment and accumulate in the food chain. Persistent organic pollutants represent the Most harmful element for the ecosystem and for human health, for example, industrial chemicals and agricultural pesticides. I these chemicals can accumulate in fish and cause serious damage to human health. Where pesticides are used on a large-scale, groundwater gets contaminated and this leads to the chemical contamination of drinking water.
Acidification: Acidification of surface water, mainly lakes and reservoirs, is one of the major environmental impacts of transport over long distance of air pollutants such as sculpture dioxide from power plants, other heavy industry such as steel plants, and motor vehicles. This problem is more severe in the US and in parts of Europe.