the emitting of harmful and toxic substances into water sources is called as water pollution.
the contamination of water and making it unfit for drinking is called as water pollution.
some of its causes are:-
1.some human activities like in rural areas people wash their trucks,bathe their cattle etc.
2.acid rain
3.sewage and waste water
4.oceans and marine dumping
5.spilling of oil from ships into sea or ocean

Contamination of water by various means is called water pollution.
release of toxic elements into water bodies by industries.
excess use of detergents in homes.
excess use of fertilisers in fields.
oil spills by ships boats etc.