Question

how water pollution is caused? write some measures to conserve water

Answer 1

Discharge of toxic wastes into the  river 
Way : Take legal action / Treat waste 
Discharge of harmful nitrates from fertilizers due to agricultural activities
Way : Biological pest control
Discharge of animal waste from farm
Untreated sewage
Way : Treat sewage
Domestic waste
Way : Use biodegradable soaps instead of detergent

Answer 2

water pollution is caused by sewage and waste water
                                              marine dumping
                                            industrial waste
                                              radioactive waste
                                             underground storage leakages
                                             atmospheric deposition
                                             global warming
                                              eutrophication...
measures
turn off the tap while brushing
turn off the tap while washing hands
fix your leaks
water in the early morning
flush with less
choose efficient fixtures