Domestic Sewage is a primary source of the first three types of pollutant.
Pathogen or diseases causing micro-organism are excreted in the feaces of infected person and may be carried into water receiving sewage discharges. Sewage from communities with large population is very likely to contained pathogen of some type.
Sewage also carries oxygen demanding substance—the organism waste that exert a biochemical oxygen demand as they are decomposed by microbes. BOD changes the ecological balance in a body of water by depleting the Dissolved Oxygen DO content.
Nitrogen and phosphorus, the major plant nutrients are in sewage, too, as well as in runoff from farm and from suburban lawns.