WATER CONTAINS OXYGEN AND FIRE NEEDS OXYGEN..THEN ALSO WHY IT IS USED FOR PUTTING OUT FIRE?

Oxygen is present in water but, in a different form. Fire cannot consume that form of oxygen. Oygen in water can only be consumed by aquatic animals such as fish with gills etc. Oxygen in water is in form of H2O so it can't be consumed by fire. Fire can only consume direct oxygen from air.