What are the major causes of water pollution? Explain.

(N/A) Water pollution arises as a result of several human activities,which leads to the presence of several undesirable substances in water. Major water pollutants with their sources have been tabulated as follows:

Pollutant	Source
Micro-organisms	Domestic sewage
Organic wastes	Domestic sewage,decaying animals and plants,animal excreta and waste,discharge from food processing industries
Plant nutrients	Chemical fertilizers
Toxic heavy metals	Chemical factories and industries
Sediments	Strip mining and soil erosion
Pesticides	Chemicals used for killing fungi,insects,weed
Radioactive substances	Mining of uranium-containing minerals
Heat	Water used for cooling in industries

Roles played by major pollutants are:
$1$. Pathogens: These water pollutants include bacteria and other organisms. They enter water from animal excreta and domestic sewage. Bacteria present in human excreta (for example,$Escherichia \ coli$ and $Streptococcus \ faecalis$) cause gastrointestinal diseases.
$2$. Organic wastes: These are biodegradable wastes that pollute water as a result of run off. The presence of excess organic wastes in water decreases the amount of oxygen held by water. This decrease in the amount of dissolved oxygen inhibits aquatic life.
$3$. Chemical pollutants: These are water soluble chemicals like heavy metals such as cadmium,mercury,nickel,etc. The presence of these chemicals (above the tolerance limit) can damage the kidneys,central nervous system,and liver.