Mention the main causes for water pollution.

(N/A) The main causes of water pollution are:
$(i)$ Pathogens: These include bacteria and other organisms that enter water through domestic sewage and animal excreta.
$(ii)$ Organic wastes: These are biodegradable wastes like leaves,grass,and trash that consume dissolved oxygen in water,leading to the death of aquatic life.
$(iii)$ Chemical pollutants: These include heavy metals like $Cd$,$Hg$,$Ni$,and $Pb$,as well as fertilizers and pesticides that contaminate water bodies.