Water that is used in houses, schools, hospitals and commercial areas ends up becoming sewage. Sewage has considerable amounts of pollutants such as organics, nitrogen, phosphorus, and pathogens. In many cases, sewage is not collected properly or even if collected it is not treated to an acceptable level. Therefore, sewage is an important source of pollution in urban areas.
Another serious burden to water quality is solid waste. When solid wastes are not collected properly or when they are dumped illegally or not properly treated they may cause pollution of both surface and groundwater.